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Descriptive  Anatomy 


OF  The; 


Human  Teeth. 


THIRD  EDITION. 


BY 


G.  V.  BLACK,  M.D.,  D.D.S.,  Sc.D. 


PUBLISHED   BY 

Thk  Wilmington  Dental  Manufacturing  Co  , 
14 13  Filbert  Street, 

PHILADELPHIA,  PA. 


Copyright,  1894,  by 

The  Wilmington  Dental  Manufacturing  Company', 

Philadelphia. 


m, 


^^w  York 


PREFACE  TO  THE  FIRST  EDITION. 


BY  my  experience  as  a  practitioner,  as  a  teacher,  and 
in  my  intercourse  with  fellow-practitioners,  I  have 
become  convinced  of  a  serious  defect  in  the  teachino- 
of  the  details  of  the  anatomy  of  the  teeth,  and  in 
the  systematization  of  the  terms  used  in  their  description. 
This  defect  has  been  a  constant  drawback  at  the  chair,  in  the 
laboratory,  and  most  of  all,  in  the  college.  The  object  of 
the  present  volume  is  to  remedy,  in  a  measure,  this  defect. 
To  this  end  I  have  had  constantly  in  view  the  needs  of  the 
dental  student  and  practitioner. 

We  have  heretofore  had  excellent  general  descriptions  in 
human  and  comparative  dental  anatomy ;  but  these  have 
dealt  principally  with  the  general  forms  of  the  dentitions  of 
the  mammalia  and  other  orders  of  animate  beings,  rather 
than  with  specific  descriptions  of  the  forms  of  the  various 
surfaces  and  surface  markings,  making  up  the  sum  of  the 
forms  of  the  individual  teeth  of  man.  Valuable  as  these 
works  have  been,  they  have  left  the  acquirement  of-a knowl- 
edge of  the  details  of  the  specific  forms  of  the  human  teeth 
mostly  to  individual  observation.  By  this  means,  many  have 
stained  to  an  excellent  perception  of  the  various  forms  of 
the  human  teeth;  but  it  is  not  reasonable  to  suppose  the 
profession  generally  will  do  this  without  some  fixed  guide. 
"What  the  dental  student  wants  most  in  the  college,  and  in 
the  ofiice,  is  a  systematized  nomenclature  of  the  several  parts 
of  the  teeth  in  detail ;  and  such  a  description  as  will  call  his 
attention  successively  to  every  part  of  each  tooth,  as  Grray,  in 
nis  Anatomy,  has  called  attention  to  every  2^art  of  each 
bone,  however  apparently  unimportant.  It  should  be  re- 
membered that  anatomy  is  not  to  be  learned  from  books 

III 


IV  PREFACE. 


alone,  but  also  by  bringing  the  parts  to  be  studied  into  view, 
and  closely  examining  tliem  in  connection  with  the  descrip- 
tions given.  Any  one  who  may  read  the  present  volume 
without  a  reasonable  number  of  human  teeth  of  each  denomi- 
nation before  him  for  examination  and  comparison,  will  be 
but  partially  benefited. 

It  has  been  my  object  to  systematize  the  nomenclature 
mostin  vogue  with  the  profession,  whenever  practical,  rather 
than  to  introduce  new  terms.  However,  the  reader  will  find 
a  few  new  terms,  and  possibly  a  few  old  ones  that  are  used 
differently  from  the  former  custom.  The  terms  up  and 
down,  to  indicate  direction  or  parts  of  teeth,  are  abandoned, 
because  of  their  ambiguity.  In  a  few  instances,  new  forms 
of  old  words  have  been  used,  especially  to  avoid  the  terms 
inner,  outer,  backward,  forward,  etc.,  which  are  so  often  mis- 
leading. The  words  mesial,  distal,  labial,  buccal,  lingual, 
etc.,  are  used  as  adverbs  of  direction  by  adding  ly,  or  the 
same  thing  is  accomplished  by  the  use  of  the  preposition  to. 
It  is  as  easy  to  say  of  a  cavity  that  it  extends  far  beyond, 
beyond,  to,  nearly  to,  or  to  the  gingival  line,  as  to  say  it  ex- 
tends up  or  down,  etc.,  and  the  meaning  will  not  be  mistaken  ; 
or  to  say  that  a  cavity  extends  distally,  or  to  the  distal,  or 
lingually,  or  to  the  lingual,  instead  of  backward,  or  inward, 
either  of  which  has  difl:erent  meanings  in  difi:erent  situa- 
tions. The  best  rule  is  to  use  no  extraneous  object  in  the 
designation  of  the  parts  of,  or  direction  on,  the  surface  of  a 
tooth  ;  but  to  confine  the  phraseology  to  the  specific  and 
well-defined  terms  applied  to  its  several  parts.  The  back 
part  of  a  molar  would  not  mean  the  same  relative  part  as  the 
back  part  of  an  incisor.  In  many  such  ways  the  author  has 
endeavored  to  systematize,  and  make  more  definite,  the 
phraseology  applied  to  the  teeth  without  going  to  extremes, 
knowing  well  that  forms  of  language  once  in  use  can  be  im- 
proved more  easily  than  they  can  be  displaced  by  new  terras, 
thous!;h  more  exact. 


PREFACE, 


The  absence  of  a  Bibliography  may  be  noted.  The  plan 
and  object  of  this  work  has  not  seemed  to  call  for  many 
references  to  authorities.  This  does  not  imply,  ho\yever, 
that  authors  who  have  preceded  me,  as  Fox,  Carabelli, 
Tomes,  Wedl,  Judd,  Wortman,  and  many  others,  to  whom 
we  are  greatly  indebted,  have  been  either  overlooked  or 
ignored. 

The  illustrations,  have  all  been  made  by  the  author  for 
the  purpose  of  illustration,  rather  than  as  works  of  art. 
After  experimenting  with  the  various  plans  of  the  manage- 
ment of  light  and  shade,  diffused  light  has  been  used  because 
more  detail  could  be  shown,  especially  in  the  difficult  task  of 
illustrating  the  occlusal  surfaces  of  the  teeth.  Each  picture 
of  a  tooth,  in  all  its  details,  is  drawn  from  accurate  measure- 
ments of  the  particular  tooth  in  hand. 

Much  of  dental  histology  might  properly  find  place  in 
this  book ;  but  that  subject  is  well  represented  by  others. 
Malforms  of  the  teeth,  supernumerary  teeth,  and  variations 
of  arrangement,  belong  to  the  subject  of  irregularities,  which 
is  amply  treated  by  several  authors.  My  aim  has  been  to 
confine  the  book  strictly  to  normal  macroscopic  anatomy. 
However,  a  very  serious  difficulty,  which  has  always  met  the 
dental  anatomist,  has  been  the  variations  of  form  in  teeth 
of  the  same  denomination.  The  endeavor  has  been  to  sys- 
tematize these  under  one,  two,  or  more  typical  forms  of  each 
tooth,  or  its  lobes,  and  point  to  the  character  of  the  changes 
which  occur.  This  has  occasionally  led  to  the  mention  of 
abnormal  forms. 

The  reader  will  find  scattered  through  the  work  some 
hints  with  regard  to  the  practical  bearing  of  anatomical 
points  on  operative  procedures,  which,  it  is  hoped,  will  be  of 
value. 


PREFACE  TO  THE  SECOND  EDITION. 


THE  rapid  sale  of  the  first  edition  of  this  work  has 
shown  an  appreciation  of  a  need  for  a  more  com- 
plete anatomical  description  of  the  human  teeth. 
In  preparing  the  work  for  a  second  edition,  the  aim 
has  been  to  render  the  original  design  more  complete  in  its 
details,  and  to  make  such  verbal  alterations  as  would  better 
fit  it  for  the  text-book  for  the  college,  and  for  reference  by 
the  practitioner.  The  most  notable  changes  are  in  the  sec- 
tion on  nomenclature ;  and  these  are  confined  to  additional 
explanations  of  words  and  phrases.  For  the  convenience  of 
students  a  brief  glossary  has  been  added. 

A  number  of  the  illustrations  have  been  redrawn,  and 
one  has  been  added.  Some  of  the  numbers  of  the  illustra- 
tions have  been  changed  to  render  them  consecutive ;  but 
the  numbering  of  the  paragraphs  remains  unchanged.  Im- 
portant words,  especially  the  subjects  of  paragraphs  and 
technical  words  the  first  time  used,  have  been  printed  in 
bold-faced  type.  This,  it  is  hoped,  will  be  of  advantage  to 
the  student,  and  especially  convenient  for  reference. 

Valuable  aid  in  the  preparation  of  the  work  for  reissue 
has  been  rendered  by  Mr,  I,  W,  Davenport,  Drs.  D.  M.  Cat- 
tell,  Edmund'Noyes,  and  C.  N.  Johnson.  G,  V,  B. 

Jacksonville,  III.,  July  15th,  1891, 
VI 


PREFACE  TO  THE  THIRD  EDITION. 


THE  continued  favor  with  which  this  work  is  received 
by  the  profession  has  made  another  edition  neces- 
sary. In  preparing  this  the  endeavor  has  been  to 
improve  the  detail  without  changing  the  form. 
The  principal  changes  will  be  found  in  the  nomenclatnre. 
The  steady  progress  of  dental  nomenclature  toward  more 
exact  forms  demands  this.  It  must  now  be  recognized  tliat 
we  have  two  distinct  forms  of  dental  nomenclature,  the  one 
used  in  comparative  dental  anatomy,  the  other  in  human 
dental  anatomy  for  the  purposes  of  dentistry.  The  one  is 
adapted  to  the  description  of  the  teeth  of  the  various 
animals,  including  the  teeth  of  man  when  his  teeth  are 
treated  of  in  the  comparative  sense ;  the  other  is  suited  ta 
the  teeth  of  man  when  the  more  exact  and  detailed  descrip- 
tions necessary  to  operative  dentistry  are  presented.  These 
word-forms  necessarily  become  the  basis  of  much  of  the 
nomenclature  of  operative  dentistry.  An  extended  examina- 
tion of  dental  literature  shows  that  up  to  a  recent  period,, 
writers  on  operative  dentistry  had  named  more  than  tAvice 
as  many  points  on  the  teeth  than  had  writers  on  dental 
anatomy.  This  fact  shows  the  necessity  that  had  existed  for 
the  more  extended  and  systematized  presentation  of  the  sub- 
ject of  dental  anatomy,  and  the  closer  systematization  of  its 
nomenclature.  However,  the  reader  will  find  the  changes 
introduced  limited  to  one  new  word,  axial ;  two  new  word- 
forms,  occlusal  in  place  of  occluding^  and  incisal  in  compound 
forms,  and  the  completion  of  the  systematization  of  t^  e 
names  of  the  angles  of  the  teeth.  This  latter  has  required 
but  few  word  changes  in  the  text. 

Improvement  has  also  been  made  in  some  of  the  descrip- 
tions, and  a  number  of  new  illustrations  have  been  added. 

G.  V.  B. 

Jacksonville,  III.,  August  21st,  1894. 

VII 


GLOSSARY. 


Alveolus.  (PI.  Alveoli.)  A  socket:  The  cavity  in  the 
process  of  the  maxillaiy  bone  in  which  the  root  of  a  tooth 
is  fixed. 

Alveolar  process.  The  projection  of  the  maxillary 
bones  which  envelops  the  roots  of  the  teeth  and  forms  their 
alveoli. 

Angle.  The  line,  or  point,  where  two  or  more  surfaces 
of  the  teeth  join.  The  mesial  and  buccal  surfaces  join  in  the 
formation  of  the  mesio-baccal  angle.     (See  Par.  7.) 

Apex.     The  terminal  end  of  the  root  of  a  tooth. 

Apical  foramen.  The  minute  opening  of  the  pulp 
canal  at  the  apex  of  the  root  of  a  tooth.     (See  Par.  153.) 

Apical  space.  The  space  between  the  bone,  or  wall  of 
the  alveolus,  and  the  apex  of  the  root  of  a  tooth.  This 
space  is  filled  with  the  soft  tissues  of  the  peridental  mem- 
brane, and  is  the  seat  of  alveolar  abscess. 

Axial  Angle.  The  line  angles  that  are  parallel  with 
the  lonoj  axes  of  the  teeth  are  called  axial  ansrles.  Thev  are 
the  mesio-buccal,  and  mesio-labial,  disto-buccal,  and  disto- 
labial,  mesio-lingual  and  disto-lingual  angles. 

Axial  surfaces.  Those  surfaces  of  the  teeth  that  are 
^Darallel  with  their  long  axes.  They  are  labial,  buccal, 
lingual,  mesial,  and  distal  surfaces. 

Axial  walls.  Of  pulp  chambers.  Those  walls  that  are 
parallel  with  the  long  axes  of  the  teeth  ;  the  mesial,  distal, 
buccal,  and  lingual  walls. 

Bell  crowned.  A  tooth  in  which  the  mesio-distal  di- 
ameter of  the  crown  is  much  greater  than  that  of  the  neck. 

VIII 


GLOSSARY.  IX 


Bicuspid.  A  tooth  with  two  cusps.  They  are  also  called 
pre-molars.  There  are  eight  hicuspids ;  two  on  each  side  of 
the  upper  jaw,  and  two  on  either  side  of  the  lower  jaw- 
They  are  named  right  and  left  upper  first  and  second,  and 
right  and  left  lower  first  and  second  bicuspids.  They  are 
situated  between  the  cuspids  and  molars. 

Border,  of  the  alveolar  process.  The  thin  edge  of  the 
alveolar  process  surrounding  the  necks  of  the  teeth. 

Buccal.     Pertaining  to  the  cheek.     Toward  the  cheek. 

Buccal  surface.  The  surface  of  a  tooth  next  to  the 
■cheek. 

Bucco-gingival  ridge.  A  prominent  ridge  near  the 
gingival  line  on  the  buccal  surface  of  the  deciduous  molars. 
It  is  especially  prominent  on  the  first  deciduous  molars. 

Bucco-lingual.  From  the  cheek  toward  the  tongue;  as 
the  bucco-lingual  diameter  of  the  crown  of  a  lower  first  molar. 

Canal.     See  Root  Canal. 

Cementum.  A  tissue  resembling  bone  which  forms  the 
outer  surface  of  the  roots  of  the  teeth. 

Contact  point.  The  point  on  the  proximate  surface  of 
a  tooth  which  touches  a  neighboring  tooth. 

Crown.  That  portion  of  a  tooth  which  is  covered  with 
enamel,  and  which  projects  from  the  tissues  in  which  the 
root  is  fixed. 

Cutting  edge.  The  edge  formed  by  the  junction  of  the 
labial  and  lingual  surfaces  of  the  incisor  and  cuspid  teeth. 
In  the  cuspids  the  edge  is  raised  to  a  point  near  its  center. 

Cusp.  A  pronounced  elevation,  or  point,  on  the  surface 
of  a  tooth,  more  especially  on  the  occlusal  surface. 

Cuspid.  A  tooth  with  one  point,  or  cusp.  There  are 
four  cuspids:  one  on  either  side  in  each  jaw,  situated  at  the 
corners  of  the  mouth. 

Deciduous  teeth.  The  teeth  of  the  child  which  are 
shed  to  give  place  to  the  permanent  teeth.  They  are  also 
called  temporary  teeth. 


GLOSSARY, 


Dentine.  The  tissue  of  which  the  main  body  of  a  tooth 
is  formed. 

Developmental  grooves.  Fine  depressed  lines  in  the 
enamel  of  a  tooth  which  mark  the  junction  of  its  lobes. 
(See  Pars.  21  and  60.) 

Developmental  lines.     See  developmental  grooves. 

Distal.  Away  from  the  median  line  of  the  face  follow- 
ing the  curve  of  the  dental  arch.  The  surface  of  a  tooth 
most  distant  from  the  median  line.     (See  Par.  5.) 

Distally.  A  direction  away  from  the  median  line  of 
the  face  following  the  curve  of  the  dental  arch. 

Distal  angle.  A  contraction  of  disto-incisal  angle. 
Used,  also,  instead  of  disto-bucco-occlusal  angle  (q.  v.). 

Disto-buccal  angle.  The  angle  formed  by  the  union  of 
the  distal  and  buccal  surfaces  of  the  bicuspids  and  molars. 

Disto-bucco-occlusal  angle.  The  angle  or  corner  of  a 
bicuspid  or  molar  tooth  formed  by  the  juncrion  of  the  angles 
of  its  distal,  buccal,  and  occlusal  surfaces  at  a  point. 

Disto-incisal  angle.  The  angle  or  corner  of  an  incisor 
or  cuspid  tooth  formed  by  the  junction  of  the  distal  surface 
and  cutting  edge,  or  incisal  surface. 

Disto-labial  angle.  The  angle  formed  by  the  union  of 
the  distal  and  labial  surfaces  of  the  incisors  and  cusj^ids. 

Disto-lingual  angle.  The  angle  formed  by  the  union  of 
the  distal  and  lingual  surfaces  of  any  of  the  teeth. 

Disto-linguo-occlusal  angle.  The  angle  or  corner  of  a 
bicuspid  or  molar  tooth  formed  by  the  junction  of  the  angles 
of  its  distal,  lingual,  and  occlusal  surfaces  at  a  point.  Rarely 
used. 

Disto-occlusal  angle.  The  angle  formed  by  the  union 
of  the  distal  and  occlusal  surfaces  of  the  bicuspids  and 
molars. 

Enamel.  A  very  hard  tissue  covering  the  crown  of  a 
tooth. 

Fissure.     A  fault  in   the  surface  of  a  tooth  caused  by 


GLOSSARY.  XI 


the  imperfect  joining  of  the  enamel  of  the  different  lobes. 
Fissures  occur  along  the  lines  of  the  develoj3mental  grooves. 

Fossa.  (PI.  Fossa\)  A  round,  or  angular  depression  in 
the  surface  of  a  tooth.  Foss?e  occur  mostly  in  the  occlusal  sur- 
faces of  the  molars,  and  in  the  lingual  surfaces  of  the  incisors. 

Gingiva.  (PL  Gingivae.)  The  portion  of  gum  tissue 
enveloping  the  necks  of  the  teeth  crown-wise  from  the  attachr 
ment  at  the  o-ino-ival  line.     The  free  marocin  of  the  sum. 

Gingival.  Pertaining  to  the  gingival  line  ;  as  the  curva- 
ture of  the  gingival  Hne,  gingival  margin,  etc. 

Gingival  curvature.  The  deviation  of  the  gingival  line 
from  the  horizontal  in  its  course  around  the  neck  of  a  tooth. 

Gingival  line.  The  line  around  the  neck  of  a  tooth  at 
which  the  gingiva  is  attached.  The  line  of  junction  of  the 
enamel  and  cementum. 

Gingival  margin.  The  portion  of  the  crown  of  a  tooth 
next  to  the  gingival  line. 

Gingivally.  A  direction  from  any  part  of  the  crown 
toward  the  gingival  line  of  a  tooth. 

Groove.  A  long-shaped  depression  in  the  surface  of  a 
tooth.     (See  Par.  11.) 

Horn.  A  slender,  or  blunt  pointed  process  of  the  pulp 
of  a  tooth  extending  toward  the  point  of  a  cusp. 

Incisal.  The  cutting  edges  of  the  incisors  and  cuspids 
are  regarded  as  incisal  surfaces. 

Incisal  margin.  That  margin  of  a  surface  of  an  incisor 
or  a  cuspid  tooth  formed  by  the  incisal  surface  or  cutting 
edge  ;  as  the  incisal  margin  of  the  labial  surface  of  the  central 
incisor. 

Incisor.  A  tooth  with  a  cutting  edge.  There  are  four 
incisors  in  the  upper  jaw%  and  four  in  the  lower  jaw.  They 
are  called  the  upper  and  lower  right  and  left  central,  and  the 
upper  and  lower  right  and  left  lateral,  incisors. 

Inclination.  Of  &■  tooth:  The  deviation  of  the  long 
axis  of  a  tooth  from  the  perpendicular  line ;  as  the  mesial 


XII  GLOSSARY, 


inclination  of  the  incisors.  (See  Par.  191.)  Of  a  surface :  The 
deviation  of  a  portion  of  the  surface  of  a  tooth  from  the 
general  plane  of  that  surface. 

Incline.     See  Inclination. 

Interproximate  space.  The  V-shaped  space  bounded 
by  the  proximate  surfaces  of  adjoining  teeth,  and  the  border 
of  the  septum  of  the  alveolar  process  between  their  necks. 
•JSTormally  this  space  is  filled  with  gum  tissue.  (See  Par. 
193.) 

Labial.     Pertaining  to  the  lips.     Toward  the  lips. 

Labial  surface.  The  surface  of  a  tooth  next  to  the  lips. 
The  incisors  and  cuspids  have  labial  surfaces. 

Labially.     A  direction  toward  the  lips. 

Labio-lingual.  From  the  lips  toward  the  tongue;  as 
the  labio-lingual  diameter  of  the  central  incisor. 

Labio-lingually.  A  direction  from  the  lips  toward  the 
tongue. 

Line  angles.  Of  the  teeth:  Those  angles  formed  by 
the  junction  of  two  surfaces  along  a  line;  as  the  mesio-buc- 
cal  angle,  disto-buccal  angle,  etc. 

Lingual.  IText  to,  or  toward  the  tongue ;  as  lingual 
surface. 

Lingually.     A  direction  toward  the  tongue. 

Lingual  Surface.  A  surface  of  a  tooth  next  to  the 
tong-ue.     All  of  the  teeth  have  linj^ual  surfaces. 

Linguo-gingival  fissure.  A  fissure  occurring  occasion- 
ally in  the  lingual  surface  of  the  upper  incisors.  It  usually 
separates  the  lingual  lobe  from  one  of  the  marginal  ridges 
and  extends  into  the  cementum.     (See  Fig.  10.) 

Linguo-gingival  ridge.  A  ridge  near  the  gum  on  the 
lingual  surface  of  the  incisors  and  cuspids.  It  is  on  the  lin- 
gual lobe.     (See  Par.  21.) 

Lobe.  A  division  of  a  tooth  formed  from  a  separate 
point  of  the  beginning  of  calcification.  (See  Pars.  21  and 
69.) 


GLOSSARY.  XIII 


Mammelons.  The  three  rounded  prominences  seen  on 
the  cutting  edges  of  the  incisors  when  they  first  come 
through  the  gums.     (E.  Magitot.) 

Marginal  Ridge.  The  ridges,  or  elevations  of.  enamel 
on  the  margins  of  the  occlusal  surface  of  the  bicuspids  and 
molars,  and  on  the  mesial  and  distal  margins  of  the  lingual 
surface  of  the  incisors  and  cuspids. 

Median  line.  The  anterio-posterior  perpendicular  cen- 
tral line  of  the  body. 

Mesial.  Toward  the  median  line.  Those  surfaces  of 
the  teeth  which,  as  they  stand  in  the  arch,  and  following  its 
curve,  are  toward  the  median  line,  are  called  mesial  surfaces. 

Mesial  angle.  A  contraction  of  mesio-incisal  angle,  also 
of  mesio-hucco-occlusal  angle  (q.  v.). 

Mesially.     Toward  the  median  line. 

Mesio-buccal  angle.  The  angle  formed  by  the  union  of 
the  mesial  and  buccal  surfaces  of  the  bicuspids  and  molars. 

Mesio-bucco-occlusal  angle.  The  angle  or  corner 
formed  by  the  junction  at  a  point  of  the  angles  of  the  mesial, 
buccal,  and  occlusal  surfaces  of  the  bicuspids  and  molars. 

Mesio-distal.  From  mesial  to  distal;  as,  the  mesio-dis- 
tal  diameter  of  the  lower  first  molar. 

Mesio-incisal  angle.  The  angle  or  corner  formed  by 
the  junction  of  the  mesial  surface  and  cutting  edge,  or  incisal 
surface,  in  the  incisors  and  cuspids. 

Mesio-labial  angle.  The  angle  formed  by  the  union  of 
the  mesial  and  labial  surfaces  of  the  incisors  and  cuspids. 

Mesio-lingual  angle.  The  angle  formed  by  the  union  of 
the  mesial  and  lingual  surfaces  of  the  teeth. 

Mesio-lingual  groove.  A  developmental  groove  running 
from  the  mesial  surface  diagonally  to  the  lingual  surface  in 
upper  first  molars  that  have  the  fifth  cusp.     (See  Par.  69.) 

Mesio-linguo-occlusal  angle.  The  angle  or  corner 
formed  by  the  junction  of  the  angles  of  the  mesial,  lingual,  and 
occlusal  surfaces  of  the  bicuspids  and  molars.    Rarely  used. 


XIV  GLOSSARY. 


Mesio-occlusal  angle.  The  angle  formed  by  the  union 
of  the  mesial  and  occlusal  surfaces  of  the  bicuspids  and 
molars. 

Neck.  That  portion  of  the  tooth  which  forms  the  junc- 
tion of  the  crown  and  root. ' 

Otlique  ridge.  A  rido;e  running  obliquely  across  the 
occlusal  surface  of  the  upper  molars.  It  is  formed  by  the 
union  of  the  triangular  ridge  of  the  disto-buccal  cusp  with 
the  distal  portion  of  the  ridge  forming  the  mesio-lingual 
cusp. 

Occlude.     To  shut.     To  close. 

Occlusal  surface.  That  surface  of  a  bicuspid  or  molar 
tooth  lhat  makes  contact  with  a  tooth  of  the  opposite  jaw 
when  the  mouth  is  closed. 

Permanent  teeth.  The  teeth  of  adult  age  as  distin- 
guished from  the  temporary,  or  deciduous  teeth. 

Pit.  A  sharp,  pointed  depression  in  the  enamel.  Pits 
occur  mostly  where  several  develoj^mental  grooves  join ;  as 
in  the  occlusal  surfaces  of  the  molars,  and  at  the  endings  of 
the  buccal  grooves  on  the  buccal  surfaces  of  the  molars. 

Point  angles.  Of  the  teeth  :  Those  corners  or  angles 
formed  by  the  junction  of  the  angles  of  three  surfaces  at  a 
point ;  as  the  disto-bucco-occlusal  angle,  the  mesio-bucco- 
occlusal  angle,  etc. 

Point  of  proximate  contact.  The  point  at  which  the 
proximate  surface  of  a  tooth  touches  the  proximate  surface 
of  a  neighboring  tooth. 

Proximate  contact.  The  contact,  or  touching,  of  the 
proximate  surfaces  of  neighboring  teeth. 

Proximation.  The  near  approach,  or  contact,  of  the 
proximate  surfaces  of  the  teeth. 

Proximate  surface.  The  surface  of  a  tooth  which  lies 
next  to  another  tooth.     (See  Par.  5.) 

Pulp.  The  soft  tissue  that  fills  the  pulp  chambers  and 
root  canals  of  the  teeth. 


GLOSSARY.  XV 


Ridge.     A  long-shaped  elevation  on  the  surface  of  a 
tooth. 

'  Root.  That  portion  of  the  tooth  that  is  fixed  in  the 
bony  walls  of  the  alveolus,  or  socket ;  and  is  covered  with 
cementum. 

Root  canal.  The  opening  through  the  center  of  the 
long  axis  of  the  root  of  a  tooth  from  the  crown  to  the  apex. 

Rugae.  A  series  of  irregular  ridges  in  the  roof  of  the 
mouth. 

Septum.  (PI.  Septa.)  A  partition:  That  portion  of 
the  alveolar  process  which  lies  between  the  roots  of  the  teeth 
separating  their  alveoli. 

Succedaneous  teeth.  Those  of  the  permanent  teeth 
which  succeed,  or  take  the  places  of,  the  temporary  teeth. 

Sulcate  groove.     A  groove  following  the  bottom  of  a 

sulcus. 

Sulcus.  (PI.  Sulci.)  A  notable  long-shaped  depression 
in  the  surface  of  a  tooth  the  inclines  of  which  meet  at  an 
angle.  A  sulcus  has  a  developmental  groove  at  the  junction 
of  its  inclines. 

Supplemental  groove.  A  shallow  long-shaped  depression 
in  the  surface  of  a  tooth,  generally  with  a  smoothly  rounded 
bottom.  Supplemental  grooves  differ  from  developmental 
grooves  in  that  they  do  not  mark  the  junction  of  lobes. 

Supplemental  lobe.  A  lobe  that  does  not  belong  to  the 
typical  form  of  the  tooth  ;  an  additional  lobe. 

Supplemental  ridge.  A  ridge  on  the  surface  of  a  tooth 
that  does  not  belong  to  the  typical  form  of  the  tooth ;  an 
additional  ridge. 

Temporary  teeth.     See  deciduous  teeth. 

Thick-necked.  A  tooth  in  which  the  mesio-distal  diam- 
.  eter  of  the  neck  is  nearly  equal  to  that  of  the  crown.  (See 
bell  crown.) 

Thirds.  Division  of  a  crown  of  a  tooth;  as  to  length, 
into  occlusal,  or  incisal  third,  middle  third,  and  gingival 


XVI  GLOSSARY. 


third  ;  as  to  mesio-distal  breadth,  into  mesial  third,  middle 
third,  and  distal  third. 

Transverse  ridge.  A  ridge  formed  of  two  triangular 
ridges,  which  join  to  form  a  continuous  ridge  across  the 
occlusal  surface  of  a  tooth. 

Triangular  ridge.  A  ridge  running  from  the  point  of  a 
cusp  toward  the  central  portion  of  the  occlusal  surface  of  a 
tooth. 

Tubercle.  A  slight  rounded  elevation  on  the  surface  of 
a  tooth.  Tubercles  occur  frequently  on  the  linguo-gingival 
ridge  of  the  incisors,  and  occasionalh'  upon  various  parts  of 
other  teeth.  They  are  deviations  from  the  typical  tooth 
forms. 


DENTAL  ANATOMY. 

NOMENCLATURE. 

1.  Man's  food  is  both  animal  and  vegetable,  and  his 
teeth  are  so  formed,  as  to  enable  him  to  readily  masticate 
either  kind  ;  therefore,  his  teeth  differ  from  those  of  both  the 
carnivorous  and  herbivorous  animals,  and  form  the  type  of 
the  omnivora.  They  are  formed  for  cutting,  tearing,  and 
comminuting  many  kinds  of  food.  The  incisors,  situated 
anteriorly,  have  edges  for  cutting ;  the  cuspids  and  bicus- 
pids, at  the  angles  of  the  mouth,  have  fairly  sharp,  though 
not  very  long,  points  or  cusps,  suited  for  tearing ;  while 
the  molars,  situated  in  the  posterior  part  of  the  mouth, 
have  broad,  tuberculated  surfaces,  which  serve  well  to  grind 
or  comminute  the  more  solid  masses.  The  forms  of  the  teeth 
of  man  indicate  a  design  that  his  food  should  be  taken  in 
rather  small  masses,  considered  from  the  standpoint  of  the 
habits  of  animals  in  general,  and  that  it  should  be  very 
thoroughly  commingled  with  saliva  before  being  passed  to 
the  stomach. 

2.  The  adult  has  thirty-two  teeth :  four  incisors,  two 
cuspids,  four  bicuspids,  and  six  molars  in  each  jaw.  Scien- 
tific men  express  the  denomination  and  number  of  the  teeth  of 
the  mammalia  by  formulae,  in  which  the  denomination  is 
represented  by  the  initial  letter,  followed  by  a  horizontal 
line,  with  the  number  of  that  kind  of  teeth  on  one  side  of 
the  upper  jaw  written  above  the  line,  and  the  number  m  the 
lower  jaw  written  below  the  line.  The  dental  formula  of 
man  is  written  thus  : 

I  f  C  I  B  f  M  I  =  32. 
This  formula  is  read  thus:    Incisors,  two  upper  and  two 
lower ;   cuspids,  one  upper  and  one  lower ;  bicuspids,  two 

B  1 


NOMENCLATURE, 


upper  and  two  lower ;  molars,  three  upper  and  three  lower ; 
sixteen  on  one  side.  As  the  opposite  side  has  the  same,  the 
full  number  is  thirty-two.  The  teeth  are  composed  of  four 
tissues :  Enamel,  w^hich  covers  the  crown ;  dentine,  which 
forms  the  body  of  both  crown  and  root ;  cementum,  w^hich 
covers  the  root  and  joins  with  the  enamel  at  the  gingival 
line,  or  neck  of  the  tooth ;  and  pulp  tissue,  which  fills  the 
central  cavity  of  the  dentine. 

3.  Each  tooth  presents  for  description  certain  charac- 
ters common  to  all,  such  as  crown,  neck  or  gingival  line, 
root,  pulp-chamber,  canal,  and  surfaces  of  crown  and  root. 
The  crown  of  a  tooth  is  that  part  which  projects  beyond 
the  gum  tissue,  and  is  covered  wdth  enamel;  while  the  root, 
covered  with  cementum,  is  that  portion  fixed  in  the  bony 
process  of  the  jaw,  by  which  the  whole  tooth  is  held  securely 
in  position.  The  root  of  a  tooth  may  be  single,  as  in  the 
incisors  and  cuspids;  divided  into  two  roots,  as  in  the 
lower  molars ;  or  into  three  roots,  as  in  the  upper  molars ; 
or  into  a  greater  number,  as  in  exceptional  examples.  The 
root  is  divided  into  the  body  or  main  portion  ;  the  apex,  or 
terminal  end  of  a  root ;  and  the  neck,  which  marks  the 
junction  of  the  root  with  the  crown.  A  tooth  is  also  marked 
with  a  slight  constriction  at  the  neck,  and  by  the  junction 
of  the  enamel  with  the  cementum.  The  latter,  which  forms  a 
visible  line  encircling  the  tooth,  is  called  the  gingival  line. 
It  is  so  curved  in  its  course  as  to  present  a  convexity  toward 
the  crown  on  the  proximate  surfaces,  to  corresjDond  with  the 
line  of  the  gum  as  it  passes  over  the  alveolar  ridge  from  the 
labial  to  the  lingual  side  of  the  arch.  On  the  anterior  teeth, 
it  is  also  so  curved  in  passing  the  labial  and  lingual  surfaces 
as  to  present  a  concavity  toward  the  crown.  These  are  called 
the  curvatures  of  the  gingival  line,  or  the  gingival  curvature. 
The  neck  of  a  tooth  is  common  to  all  of  the  roots,  whatever 
the  number,  for  the  point  of  division  into  two  or  more  roots 
is  always  rootward  from  the  neck. 


NOMENCLATURE, 


4.  The  crowns  of  the  incisors  and  cuspids  present  for 
examination  four  surfaces  and  an  edge ;  and  the  crowns  of 
the  bicuspids  and  molars,  five  surfaces.  (Diagram  A.)  These 
surfaces  are  named  according  to  their  position  and  use.  Those 
of  the  incisors  and  cuspids  presenting  toward  the  lips,  are 
called  labial  surfaces ;  those  of  the  bicuspids  and  molars  pre- 
senting toward  the  cheek,  buccal  surfaces;  all  presenting 
toward  the  tongue,  lingual  surfaces,  whether  in  the  upper  or 
the  lower  jaw.*  Those  surfaces  which  come  in  contact  with 
the  opposing  teeth  in  closing  the  mouth  are  called  occlusal 
surfaces.  These  surfaces  of  the  bicuspids  and  molars  are 
also  called  grinding  surfaces. 

5.  The  surfaces  of  the  teeth  that  present  toward,  or  lie 
against,  adjoining  teeth  are  called  proximate,  or  proximal, 
surfaces.  The  proximate  surfaces  are  also  more  closely 
defined  by  the  terms  mesial  and  distal.  These  terms  have  spe- 
cial reference  to  the  position  of  the  surface  relative  to  the  cen- 
tral or  the  median  line  of  the  face.  This  line  is  drawn  along, 
the  suture  uniting  the  superior  maxillary  bones,  or  perpendic- 
ularly through  the  center  of  the  face  and  mouth,  and  passes 
between  the  central  incisors  of  both  the  upper  and  lower  jaws. 
Those  proximate  surfaces  which,  as  they  are  placed  in  the  arch, 
and  following  its  curve  ^  are  toward  the  median  line,  are  called 
mesial  surfaces ;  and  those  most  distant  from  the  median 
line  are  called  distal  surfaces.  The  mesial  surfaces  of  the 
central  incisors,  both  upper  and  lower,  proximate  each  other; 
but  in  all  other  cases  a  mesial  surface  proximates  a  distal. 
Also,  a  distal  surface  always  proximates  a  mesial  surface, 
except  those  of  the  third  molars,  upper  and  lower,  which 
have  no  distal  proximating  teeth.  The  points  at  which  the 
proximate  surfaces  touch  each  other  as  the  teeth  stand  in  the 
line  of  the  arch,  are  called  the  points  of  proximate  contact, 
or  simply  contact  points. 

*Some  authors  use  the  term  "  palatine  surfaces"  for  those  of  the  upper  jaw,  and 
"  lingual "  for  those  of  the  lower.    This  seems  unnecessarv. 


NOMENCLATURE. 


For  convenience  in  designating  the  different  parts  of  the 
crowns  of  the  teeth,  they  may  be  divided  into  thirds,  in  any 
one  of  three  directions:  Tnciso,  or  occliiso-gingivally  into 
incisal,  or  occlusal  third,  middle  third,  and  gingival  third; 
mesio-distally  into  the  mesial  third,  middle  third,  and  distal 
third ;  bucco-lingually  into  the  buccal  third,  middle  third, 
and  lingual  third. 

Eacji  of  the  five  surfaces  may  be  divided  into  thirds  in 
either  one  of  two  directions.  The  labial,  or  buccal,  and  the 
lingual  surfaces  are  divided  inciso-  or  occluso-gingivally^ 
into  the  incisal,  or  occlusal  third,  middle  third, and  gingival 
third:  mesio-distally  into  the  mesial  third,  middle  third,  and 
distal  third.  Mesial  and  distal  surfaces  are  divided  inciso- 
or  occluso-gingivally  into  the  incisal,  or  occlusal  third,  mid- 
dle third,  and  gingival  third  ;  bucco-lingually,  into  the  buccal 
third,  middle  third,  and  lingual  third.  The  occlut^al  surfaces 
are  divided  mesio-distally  into  the  mesial  third ,  middle  third, 
and  distal  third  ;  bucco  lingually,  into  the  buccal  third,  mid- 
dle third,  and  lingual  third.  The  cutting  edges,  or  incisal 
surfaces  of  the  incisors  and  cuspids,  are  divided  mesio-dis- 
tally only.  These  divisions  are  the  mesial  third,  middle 
third,  and  distal  third. 

6.  The  incisors  present  a  cutting  edge  by  the  junction 
of  the  labial  and  lingual  surfaces  along  a  line.  In  the  cus- 
pids, this  joining  of  the  surfaces  to  form  an  edge  is  raised  to 
a  point  near  the  center  of  its  length,  forming  a  cusp,  hence 
the  term  cus^Did,  a  tooth  with  one  point.  The  cutting  edges 
of  the  incisors,  and  the  occlusal  surfaces  of  the  bicuspids 
and  molars,  come  in  contact  with  the  similar  surfaces  of  the 
teeth  of  the  opposing  jaw  when  the  mouth  is  closed,  as  in 
the  act  of  biting.  The  incisors  and  cuspids  of  the  upper  jaw 
do  not  occlude  exactly  on  the  cutting  edges  or  cusps,  but 
generally  just  back  of  them  ;  though  for  convenience,  the 
term  occlusal  may  be  applied  to  them  as  if  they  did,  though 
they  will  generally  be  called  cutting  edges,  and  the  adjective 


NOMENCLATURE. 


form  incisal  will  be  used  in  all  compound  words.  The 
occlusal  surfaces  of  the  bicuspids  have  two  cusps,  hence  the 
term  bicuspid,  a  tooth  with  two  points;  and  the  occlusal 
surfaces  of  the  molars  have  four  cusps,  and  sometimes  more. 

7.  The  angles  of  the  teeth  are  of  two  kinds:  Line  angles 
and  point  angles.  The  line  angles  are  formed  by  the  junction 
of  two  surfaces  along  a  line.  The  point  angles  are  formed 
by  the  junction  of  three  surfaces  forming  a  corner.  The  in- 
cisors and  cuspids  have  four,  and  the  bicuspids  and  molars 
have  eight  line  angles.  Angles  are  named  by  combining  in 
a  compound  word  the  names  of  the  surfaces  which  join  to 
form  the  angle.  The  incisors  and  cuspids  have  mesio-labial 
angles,  which  extend  from  the  catting  edge  to  the  gingival 
line  along  the  line  of  union  of  the  mesial  and  labial  surfaces. 
Also,  disto-labial  angles,  mesio-lingual  angles,  and  disto-lin- 
gual  angles,  formed  similarly  by  the  junction  of  the  surfaces 
named  in  these  compound  words. 

The  bi«-uspids  and  molars  have  mesio-buccal  angles, 
formed  by  the  junction  of  the  mesial  and  buccal  surfaces 
along  a  line  from  the  occlusal  surface  to  the  gingival  line. 
Also,  disto-buccal  angles,  mesio-lingual  angles,  and  disto- 
lingual  angles,  all  of  which  are  formed  in  the  same  manner 
as  the  mesio-buccal.  These  are  called  the  axial  line  angles 
because  they  are  parallel  with  the  long  axes  of  the,  teeth. 

The  bicuspids  and  molars  have  also  four  occlusal  line 
angles,  which  are,  however,  more  generally  called  marginal 
ridges.  The  mesio-occlusal  angles  extend  bucco-lingually 
along  the  line  of  junction  of  the  mesial  and  occlusal  sur- 
faces. The  disto-occlusal  angles  are  similarly  formed.  The 
l3ucco-occlusal  angles  and  the  linguo-occlusal  angles  extend 
mesio-distally  along  the  line  of  junction  of  the  surfaces 
named  in  these  compound  words. 

The  point  angles  of  the  bicuspids  and  molars  are  four 
•occlusal  and  four  gingival.  As  these  are  formed  by  the  junc- 
tion of  the  angles  of  three  surfaces  forming  a  corner,  their 


NOMENCLATURE. 


names  are  compounds  of  the  names  of  the  three  uniting  sur- 
faces. The  mesio-bucco-occlus'al  angles  are  formed  by  the 
junction  of  the  angles  of  these  three  surfaces  at  a  point.  The 
mesio-linguo-occlusal  angles,the  disto-bucco-occlusal  angles, 
and  the  disto-linguo-occlusal  angles  are  formed  in  a  similar 
manner.  These  names  of  point  angles  are  precisely  the  same 
for  all  of  the  bicuspid  and  molar  teeth. 

The  incisors  and  cuspids  have,  on  account  of  their 
wedge-like  form,  but  two  incisal  point  angles.  These  are 
the  mesio-incisal  and  disto-incisal  angles,  which  form  the- 
corners  at  the  mesial  and  distal  terminations  of  the  incisal 
surface  or  cutting  edge. 

The  gingival  point  angles  represent  the  corners  of  the 
crowns  of  the  teeth  at  their  junction  with  the  roots  at  the 
gingival  line,  or  the  gingival  termination  of  the  axial  line 
angles;  and  are  named  precisely  as  the  axial  line  angles,, 
with  the  addition  of  the  word  gingival.  Thus,  the  incisors 
and  cuspids  have  mesio-labio-gingival  angles,  mesio-linguo- 
gingival  angles,  disto-labio-gingival  angles,  and  disto-linguo- 
gingival  angles.  These  angles  are  named  in  the  same  way 
for  the  bicuspids  and  molars,  except  that  the  word  buccal 
is  substituted  for  labial ;  thus,  mesio-bucco-gingival  angle,, 
disto-bucco-gingival  angle,  the  angles  on  the  lingual  being 
named  as  in  the  incisors.  Up  to  the  present  time  the  gin- 
gival point  angles  have  not  been  used  in  descriptions  of  the- 
teeth,  and  are  given  here  only  for  the  sake  of  complete-^ 
ness. 

When  any  individual  surface  of  a  tooth  is  considered 
alone  it  is  regarded  as  having  margins  and  angles  of  its  own,, 
or  belonging  to  it.  Each  margin  is  designated  by  the  name 
of  the  surface  with  which  it  is  joined,  except  that  toward  the 
gingival  line,  which  takes  the  name  gingival  margin.  The 
buccal  surface  of  a  bicuspid  or  molar  has  a  gingival  margin, 
a  mesial  margin,  a  distal  margin,  and  an  occlusal  margin. 
The  labial  surface  of  [an  incisor  has  a  gingival  margin,  a 


Note.— In  the  naming  of  the  surfaces  and  angles  of  the  teeth  the  crowns  are  regarded 
as  representing  cubes  with  the  angles  more  or  less  rounded,  though  they  are  named  as  if 
they  were  true  cubes.  For  this  reason  the  diagrams  here  given  for  the  explanation  of 
these  names  are  drawn  as  cubes. 

Diagram  A  (Pars.  4  and  5).— The  Surfaces  of  a  Lowek  Molar,  m,  Mesial  surface ;  I, 
lingual  surface ;  b,  buccal  surface ;  d,  distal  surface ;  o,  occlusal  suriace ;  g,  gingival 
line.  This  line  passes  entirely  around  the  tooth  at  the  junction  of  the  crown  with  the 
root. 

Diagram  B  (Par.  7).— The  Najies  and  Positions  of  the  Line  Angles  of  a  Molar. 
mb,  Mesio-buccal  angle ;  ml,  mesio-lingual-  angle ;  cJb,  disto-buccal  angle ;  dl,  disto- 
lingual  anyle ;  mo,  mesio-occlusal  angle ;  do,  disto-occlusal  angle  ;  bo,  bucco  occlusal 
angle  ;  lo,  linguo-occlusal  angle.  The  names  of  the  occlusal  line  angles  (the  last  four) 
are  seldom  used,  as  they  are  called  also  marginal  ridges. 

Diagram  C  (Par.  7).— The  Names  and  Positions  of  the  poinx  angles  of  the  Teeth. 
It  will  be  noticed  that  these  angles  are  formed  by  the  junction  of  three  surfaces  forming 
a  corner  or  point,  and  that  the  names  of  three  surfaces  form  the  name  of  the  angle. 
mbo,  Mesio-bucco-occlusal  angle ;  mlo,  mesio-linguo-occlusal  angle :  dho,  disto-bucco- 
occlusal  angle;  fZ?o,  disto  linguo-occlusal  ang;e  ;  ?)(br/,  mesio-bucco-gingival  angle;  m!g 
mesio-linguo-gingival  angle ;  dbg,  disto-bucco-gingival  angle  ;  dig,  disto-linguo-gingival 
angle. 


NOMENCLATURE.  9 


mesial  margin,  a  distal  margin,  and  an  incisal  margin.  The 
maro-ins  of  the  lino;ual  surfaces  of  all  of  the  teeth  are  named 
in  precisely  the  same  terms  as  those  of  their  buccal  or  labial 
surfaces.  Also,  the  margins  of  mesial  and  distal  surfaces 
are  named  in  the  same  terms.  A  mesial  or  distal  surface  of 
a  bicuspid  or  molar  has  a  gingival  margin,  a  buccal  margin, 
a  lingual  margin,  and  an  occlusal  margin.  The  mesial  and 
distal  surfaces  of  the  incisors  and  cuspids  have,  on  account 
of  their  triangular  form,  onlj  three  margins:  the  gingival, 
labial  and  lingual. 

The  angles  of  a  surface  of  a  tooth  are  named  by  com- 
bining the  names  of  the  margins  joining  to  form  the  angle. 
Thus,  the  buccal  surface  of  a  molar  has  four  angles,  the  mesio- 
occlusal,  disto-occlusal,  mesio-gingival,  and  disto-gingival 
angles.  All  angles  of  the  surfaces  of  the  teeth  are  named 
on  this  plan.  The  mesial  and  distal  surfaces  of  the  incisors 
and  cuspids  having  but  three  margins  have  but  three  angles: 
the  labio-gingival,  linguo-gingival,  and  incisal  angles."-  (The 
name  incisal  angle  is  an  exception  to  the  general  rule  for 
naming  angles  of  surfaces.) 

8.  A  cusp  is  a  pronounced  elevation,  more  or  less 
pointed  on  the  surface  of  a  tooth,  but  more  especially  on  the 
occlusal  surface.  A  slight  elevation  is  often  called  a  tuber- 
cle, as  that  frequently  seen  near  the  gum  on  the  lingual  sur- 
face of  the  upper  incisors.  These  are  generallj'  deviations 
from  the  typical  forms  of  the  teeth. 

9.  Long-shaped  elevations  on  the  surfaces  of  teeth  are 
called  ridges,  and  are  named  according  to  their  location  or 
form ;  as  buccal  ridge,  lingual  ridge,  and  marginal  ridge. 

*  The  student  should  note  carefully  the  difference  between  the  names  of 
the  angles  of  a  tooth  and  the  angles  of  a  surface  of  a  tooth.  To  illustrate: 
The  mesio-bucco-occlusal  angle  of  a  tooth  is  in  effect  the  bucco-occlnsal  angle 
of  its  mesial  surface,  the  mesio-buccal  angle  of  its  occlusal  surface,  or  the 
mesio-occlusal  angle  of  its  buccal  surface.  In  this  work  the  descriptions  are 
mostly  of  individual  surfaces,  hence  the  names  of  the  angles  of  surfaces  are 
much  oftener  used  than  the  names  of  the  angles  of  the  teeth. 


10  NOMENCLATURE. 


The  marginal  lidges  are  those  elevations  of  the  enamel  which 
form  the  margins  of  the  occlusal  surfaces  of  the  bicuspids 
and  molars,  and  the  mesial  and  distal  margins  of  the  lingual 
surfaces  of  the  incisors  and  cuspids.  Those  ridges  which 
descend  from  the  cusps  of  the  molars  and  bicuspids  toward 
the  central  part  of  the  occlusal  surfaces  are  called  triangular 
ridges.  They  are  so-called  because  the  typical  form  of  the 
ridges  is  usually  that  of  a  triangle.  They  are  named  after 
the  cusps  to  which  they  belong,  as  the  triangular  ridge  of 
the  mesio-buccal  cusp  of  the  upper  first  molar,  or  simply, 
mesio-buccal  triangular  rido;e.  When  a  buccal  and  a  lingual 
triangular  ridge  join  they  form  a  transverse  ridge.  In  this 
way  they  often  subdivide  the  central  fossa  of  the  lower 
molars  and  form  supplemental  fossae. 

10.  A  generally  rounded  or  angular  depression  on  the 
surface  of  a  tooth  is  called  a  fossa.  Fossse  occur  mostly  on 
the  occlusal  surfaces  of  the  molars.  When  a  notable  de- 
pression is  long- shaped  it  is  called  a  sulcus.  Some  of  these 
pass  mesio-distally  entirely  through  the  occlusal  surface  of  a 
tooth,  as  in  the  bicusjDids.  This  term  is  often  erroneously- 
applied  to  the  grooves  and  fissures. 

11.  A  shallow,  long-shaped  depression,  in  the  form  of 
a  line,  on  the  surface  of  a  tooth,  is  called  a  groove.  When 
such  a  groove  follows  the  bottom  of  a  sulcus  it  is  said  to  be 
sulcate.  When  such  a  groove  sinks  suddenly  into  the  sub- 
stance of  a  tooth  in  the  form  of  a  fault  it  is  called  a  fissure. 
The  words  sulcus,  groove,  and  fissure  are  often  used  as  if 
they  were  synonymous  and  interchangeable,  which  has  given 
rise  to  much  confusion.  It  is  necessary  that  the  distinc- 
tions made  in  their  use  in  dental  anatomy  be  well  under- 
stood. A  groove  is  a  very  fine  line  in  the  form  of  a  slight, 
sharp  depression  on  the  suface  of  the  tooth,  as  represented 
in  section  in  Diagram  D,  at  a  in  a  section  cut  at  the  point 
where  the  mesial  groove  passes  over  the  marginal  ridge  of  a 
bicuspid.     Diagram  E,  from  a  cross  section  of  a  bicuspid, 


NOMENCLATURE, 


11 


very  close  to  the  occlusal  surface  grooves  are  shown  at  a,  a. 
A  very  shallow  depression  with  rounded  bottom  is  also 
called  a  groove,  as  those  seen  on  the  labial  surfaces  of  the 
incisors.  A  sulcate  groove  is  one  that  follows  a  sulcus  of 
notable  depth,  the  inclines  of  which  approach  each  other  at 
an  angle  as  represented  in  Diagram  F,  a,  pointing  out  the 
groove,  and  c,  the  inclines  of  the  surface  of  the  tooth  which 


form  the  sulcus.  A  fissure  is  always  a  fault  in  the  enamel, 
a  point  where  the  margins  of  the  plates  of  enamel  fail  to 
unite,  as  represented  at «,  in  Diagram  G.  These  are  distinc- 
tions of  importance,  and  there  should  be  no  confusion  in  the 
use  of  the  words  by  which  we  distinguish  them.  There  are 
two  varieties  of  grooves  in  the  teeth,  diftering  essentially  in 
their  nature  and  formation.     One  class  mark  the  lines  on 


12  NOMENCLATURE. 


which  the  parts  of  the  enamel  first  formed  separately,  are 
afterward  joined,  and  are  called  the  essential  or  develop- 
mental grooves,  or  developmental  lines.  In  their  relation 
to  the  development  of  the  enamel,  they  are  of  the  same 
nature  and  resemble  the  sutures  of  the  bones  of  the  skull, 
which  mark  the  junction  of  the  separately  formed  plates. 
The  parts,  or  divisions,  of  a  tooth  outlined  by  its  develop- 
mental grooves  are  called  its  lobes.  Most  human  teeth  have 
four  lobes;  but  some  have  five,  and  some  only  three.  Hence, 
these  grooves  form  the  key  to  much  of  descriptive  dental 
anatoni}^ ;  and  when  they  can  be  traced,  enable  the  anatom- 
ist to  unravel  complex  forms,  and  assign  irregularly -formed 
teeth  to  the  groups  to  which  they  belong,  to  pro[)erl3^  name 
their  individual  parts,  and  identify  any  additional,  acci- 
dental, or  unusual  forms  of  parts  that  may  have  become  inter- 
mingled in  the  accident  of  a  faulty  formation.  These  devel- 
opmental grooves,  or  iines,  are  subject  to  fissures,  which 
occur  when,  from  any  cause,  there  is  a  failure  of  perfect 
union  of  the  parts,  leaving  a  fault. 

12.  The  other  class  of  grooves  have  no  especial  relation 
to  the  developmental  lines,  and  are  called  supplemental 
grooves.  These  are  aptly  described  as  wrinkles  in  the  enamel, 
which,  in  fact,  many  of  them  are.  But  some  are  so  constant 
in  their  location  and  form  as  to  make  up  a  portion  of  the 
typical  tooth-form.  The  supp].emental  grooves  are  usually 
shallow,  with  well-rounded  bottoms,  and  are  not  ordi- 
narily subject  to  fissure. 

13.  In  the  mesio-distal  direction  all  of  the  teeth  are  a 
little  broader  at  or  near  their  occlusal  surfaces  than  at  their 
necks;  therefore,  as  they  stand  in  the  well-formed  arch,  their 
proximate  surfaces  touch  only  at  or  near  the  occlusal  margins 
of  their  proximate  surfaces,  leaving  V-shaped  openings  be- 
tween their  necks.  These  are  called  inter-proximate  spaces. 
JSTormally,  the  inter-proximate  spaces  are  filled  with  gum 
tissue. 


MEASUREMENTS   OF    THE   TEETH.  13 


14.  The  teeth  of  different  individuals  show  considerable 
variety  of  form.  Some  persons  have  teeth  with  very  long 
crowns,  broad  in  the  mesio-distal  direction  at  their  occlusal 
surfaces  and  narrow  at  their  necks.  These  present  large 
inter-proximate  spaces.  They  are  known  as  bell-crowned 
teeth.  Again,  some  individuals  have  teeth  that,  in  their 
mesio-distal  diameter,  are  nearly  as  thick  at  their  necks  as 
at  the  occlusal  surfaces,  making  their  inter-proximate  spaces 
very  narrow,  the  teeth  almost,  or  quite,  touching  along  the 
whole  length  of  the  crown.  These  are  known  as  thick- 
necked  teeth.  The  more  common  form  is  midway  between 
these  two  extremes.  The  teeth  of  some  individuals  and 
families  have  very  long  cusps ;  those  of  others  have  very 
short  cusps.  Some  are  deeply  marked  by  grooves  and  sulci, 
and  in  those  of  others  the  grooves  and  sulci  are  shallow. 
Thus,  there  is  considerable  variety  of  contour  without  change 
of  type. 

MEASUREMENTS  OF  THE  TEETH. 

15.  In  the  following  tables  the  results  of  the  measure- 
ment of  many  teeth  of  each  denomination  are  given.  The 
numbers  measured  of  the  diff'erent  varieties  differed,  but  in  all 
denominations  they  w^ere  sufficient  to  insure  reasonable  accu- 
racy as  to  the  average  size.  There  are  three  measurements 
given,  the  average,  greatest,  and  least,  in  the  several  posi- 
tions measured.  "With  a  greater  number,  both  larger  and 
smaller  teeth  might  be  found,  so  that  the  tables  must  not 
be  taken  to  represent  the  greatest  nor  the  least  that  might 
be  obtained  ;  but  the  occurrence  of  larger,  or  longer  teeth 
must  be  rare. 

The  lines  of  measurement,  are: 

1st.  "  Length  over  all :"  Length  of  the  tooth  from  the 
cutting  edge,  or  buccal  cusp,  to  the  apex  of  the  root. 

2d.  "Length  of  crow^n:"  Length  of  the  crown  from 
the  cutting  edge,  or  buccal  cusp,  to  the  gingival  line  on  the 
labial  or  buccal  surface. 


14  MEASUREMENTS   OF    THE    TEETH. 

3d.  "Length  of  root:"  Length  of  root  from  the  gingival 
line  on  the  buccal  surface  to  the  apex  of  the  root. 

4th.  "  Mesio-clistal  diameter  of  crown : "  This  is  the 
extent  from  mesial  to  distal  in  the  greatest  diameter,  or  at 
the  points  of  proximate  contact. 

5th.  "  Mesio-distal  diameter  of  neck:  "  This  measure- 
ment was  made  at  the  gingival  line. 

6th.  "Labio-  or  bucco-lingual  diameter:"  This  meas- 
urement was  taken  at  the  greatest  diameter  of  the  crown  in 
the  direction  named.  In  the  incisors  it  was  on  the  gingival 
ridge.  In  the  bicuspids  and  molars  it  was  generally  mid- 
length  of  the  crown,  but  occasionally  it  was  near  the  gingival 
line,  especially  in  the  upper  second  and  third  molars. 

7th.  "Curvature  of  the  gingival  line:"  This  is  the 
height  or  extent  of  the  curve  of  the  gingival  line  toward  the 
cutting  edge,  or  occlusal  surface,  as  it  passes  from  labial  to 
lingual,  measured  on  the  mesial  surface. 

Having  these  tables,  the  necessity  for  giving  many 
measurements  in  the  text  is  avoided. 


MEASUREMENTS    OF    THE    TEETH. 


15 


UPPER  TEETH. 


Table  op  Measurements  of 
THE  Teeth  oe  Man,  Given 

IN      MlIvLIMETERS      AND 

Tenths  op  Mili^imetres.* 

u 

o 

□ 
h4 

22.5 
27.0 
18.0 

2 

0 

H 
OJ 

lO.O 

12  0 

8.0 

0 

■2 
0 

C5J0 

a 
>-r 

12.0 

16  0 

8.0 

d 
& 

In  u 

0  u 
■55  « 

s  a 
.2 

9.0 

10. 0 

8.0 

en   " 

y  0 

0     iH 

^  S 
.2 

'5 

6.3 
7.0 

5-5 

6  i-<' 

0  "■' 

a^ 

SB 

a 

03  a 

7.0 
8.0 
7.0 

6.0 
7.0 
5-0 

80 
9.0 

7.0 

•2  V 

-*H  a 
o"-=; 

u    Co 
"cO    00 

>  a 

UPPER  TEETH. 

s  OX) 

Central                  Average. 

central  _                 Greatest. 

Incisor.          ^^^^^ 

3-0 

4.0 
2.0 

Lateral                   Average. 

22.0 
26.0 
17.0 

8.8 

10.5 

8.0 

9-5 

12.0 

8.0 

8.2 
9.0 
7.0 

13.0 

16.0 

8.0 

17-3 
20.5 
II. 0 

6.4 
7.0 
50 

7.6 
9.0 
7.0 

4.4 
4.0 

5-2 

6.0 
4.0' 

2.8 
4.0 
2.0 

Average. 
Cuspid.                   Greatest. 
Least. 

26.5 
32.0 
20.0 

2.5 
35 

I.O 

First                       Average. 

20.6 
22.5 
17.0 

12.4 
14.0 

lO.O 

7.2 
8.0 
7.0 

4.9 
6.0 
4.0 

91 

lO.O 

8.0 

8.8 
ip.o 

7-5 

I.I 
2.0 
0.0 

Second                 r!"fS- 

B--PM-   S"'- 

21.5 
27.0 
16.0 

7.5 
9.0 
7.0 

14.0 
19.0 
lo.o 

6.8 
8.0 
6.0 

5-3 
6.5 
4-5 

0.8 

1-5 
0.0 

First                      Average 

20.8 
24.0 
17.0 

20.0 
24.0 
16.0 

17.I 
22.0 
14.0 

7-7 
9.0 
7.0 

13.2 

16.0 

lO.O 

10.7 

12.0 

9.0 

7-5 
8.0 
7.0 

11.8 
12.0 
II. 0 

2.2 
3-0 
1.0 

Second                   Average. 
Molar.            Greatest. 
Least. 

7.2 
8.0 
6.0 

13.0 

17.0 

90 

9.2 
.10.0 

7.0 

6.7 
8.0 
6.0 

II-5 
12.5 

lO.O 

1.6 
4.0 
0.0 

Third                      Average 

6.3 

8.0 
5-0 

II.4 

I5-0 

8.0 

8.6 
II. 0 

7.0 

6.1 
8.0 
5.0 

10.6 

14-5 
80 

0.7 

2.5 
0.0 

*  There  are  25.4  millimeters  to  the  inch. 


16 


MEASUREMENTS   OP   THE   TEETH. 


LOWER  TEETH. 


Table  of  Measurements  of 
theTketh  of  Man,  Given 
IN   Millimeters   and 
Tenths  of  Millimeters. 

15 
u 

o 

n 
<u 
f4 

a 

2 

a 

OJ 

1-r 

0 

2 

a 

1n  0 
0  ^, 

.2 

to  n 

0   u 

S  s 

.2 
'5 

1    u 

0    4> 

-C    03 

0) 

LOWER  TEETH. 

0 

Central                  Average 

20.7      8.8 
24.0     10.5 
16  0      7.0 

II  8 

16.0 

90 

12.7 
17  0 
II. 0 

54 
6.0 

5-0 

35 
50 
2.5 

60 

6.5 

55 

2-5 

30 

1-5 

T  ateral                     Average, 
"^''in'cisor.          Greatest. 
Least. 

21. 1 
27.0 
18.0 

25.6 
32-5 
20.0 

21.6 
26.0 
18.0 

22.3 
26.0 
18.0 

96 

12.0 

7.0 

103 

12.0 

8.0 

7.8 
9.0 
6.5 

7-9 

lo.o 

6.0 

59 
6.5 
5-0 

3-8 
50 
3-0 

6.4 

75 
60 

25 
3-5 
2  0 

Average. 
Cuspid.                   Greatest. 
Least. 

15  3 
21.0 
II. 0 

69 
90 
5-0 

5-2 

7.0 
3-0 

7-9 

lO.O 

6.0 

2.9 
40 
2.0 

First                       Average. 

14.0 
18.0 
II.c 

69 
8.0 
6.0 

4-7 
50 
4-5 

4.8 

6.5 
40 

8.5 
95 

7-5 

8.1 

85 
.8.0 

7-7 
8.0 
7.0 

80 
9.0 
7.0 

0.8 
1.5 
0.5 

Second                  ^^ff^t 

144 
17-5 
11.5 

7■^ 
8.0 

•6.5 

II. 2 
12.0 
II. 0 

10.7 
II. 0 

lO.O 

0.6 
2.0 
0  0 

First                       Average 
Molar.            g--st. 

21,0 
24  0 
18.0 

7  7 

10.0 

70 

13.2 

150 
II  0 

12.9 
14  0 
12.0 

II. 8 

17.0 

8.0 

10.3 
if-5 

lO.O 

I.I 
2.0 
0.0 

Second                  Average 
Molar.            Greatest. 
Least. 

19.8 
22.0 
18.0 

18.5 
20.0 
16.0 

6.9 
80 
6.0 

6.7 

8.0 
fc.o 

lO.I 

10.5 

95 

0.2 

I.O 

0.0 

Third                      Average 
Molar.            Greatest. 
Least. 

10.7 

12  0 

8.0 

8.3 
9-5 
50 

9.8 
10.5 
90 

0.2 

1-5 
0.0 

MEASUREMENTS    OF   THE   TEETH. 


17 


UPPER  AND  LOWER  TEETH. 


Table  of  Measurements  of 
THE  Deciduous  Teeth  of 
Man,  Given  in  Millime- 
ters AND  Tenths  of  Milli- 
meters. 

a 
4; 

i4 

0 

u 
h4 

0 

2 
0 

A 

a 

a 
«  0 

-4-)     ^ 

Is 

tn   (U 

^  a 

en  <u 

.2 

d 

11 

*?  0 

6    Vh 

Is  <u 

.2 
.  '5 

e— 1 

•2o 

Averages  Only. 

.2  ii 

rt  a 

UPPER  TEETH. 

TS 

Central  Incisor. 

16.0 

6.0 

lO.O 

6.5 

4-5      5-0 

4.0 

Lateral  Incisor. 

15.8 

5-6    11.4 

5-1 

3-7 

4.8 

3-7 

Cuspid. 

19  0 

6.5     13-5 

7.0 

■ 
51 

7.0 

5-5 

First  Molar. ' 

15.2 
17-5 

14.0 

5-1 

10. 0 

7-3 

5-2 

8.5 

6.9 

Second  Molar. 

5-7 
50 

II. 7 
9.0 

8.2 
4.2 

6.4 
3-0 

lO.O 

4.0 

8.3 

LOWER  TEETH. 

Central  Incisor. 

3-5 

Lateral  Incisor. 

15.0 

5-2 

lO.O 

4.1 
5-0 

3.0   :      4.0 

i 

3-7      4-8 

3-5 

Cuspid. 

17.0 

6.0 

II-5 

4.0 

First  Molar. 

15.8 

6.0 

9.8 

7-7 
9-9 

6.5 
7.2 

7.0 

8.7 

5.3 

Second^Molar. 

18.8; 

5-5 

II-3 

6.4 

18 


MEASUREMENTS   OF   THE    TEETH. 


UPPER  TEETH. 


Tablk  op  Measurements  of 
THE  Teeth   of  Man;   in 
Inches  and  Hundredths 
of  an  Inch. 

Id  • 
i-i 

o 

n 
h4 

2 
0 

U-i 

0 

0 

HJ 

h4 

•39 
•41 
•31 

0 
0 
u 

0 

bo 

a 

OJ 

k4 

'C   0 

en  *-i 

cu   <u 

cd 

en  -tJ 

"'5 

6    D 

X>    Cue 
cd   S 

a.S 
3  Sa 

UPPER  TEETH. 

Central                  Greatest. 
I^^i^°^-          Least. 

.88 
1.06 

.7? 

•49 
•63 
•31 

•35 
•39 
•31 

.24 

•27 
.21 

.27 

•3f 

.27 

.11 

.07 

Lateral                   cllaSt 
Incisor.           j^^^3^_ 

.86 

1.02 

.66 

•34 
.41 
•31 

•51 
•63 
•31 

•25 

.27 

•19 

•17 
.19 

•  15 

•23 
•23 
.19 

.11 

•15 

.07 

Average. 
Cuspid.                   Greatest. 
Least. 

1.04 

1.26 

•79 

•37 
.47 
•  31 

.68 
.80 
•43 

.29 

•35 

.27 

.20 
•23 
•15 

•31 
•35 
.27 

.09 
•13 
•03 

T^-     .                        Average. 

^i^^t                       Greatest. 

Bicuspid.        j^^^g^_ 

.81 
.89 
.66 

•32 
•35 
.27 

.48 
•55 
•39 

.28 
•3t 

•27 

•19 
-23 
•15 

•35 
•39 
•31 

.04 

.07 
.00 

Second                   GrelSt 
Bicuspid.       j^^^g^_ 

.84 

1.06 

.62 

.29 
.29 
.27 

•5S 
•55 
•39 

.26 
•31 
•23 

.20 
•25 
•17 

•34 

-.39 
•29 

•03 
•05 
.00 

G^st 
^ol^''-            Least. 

.81 
.94 
.66 

•30 
•35 
.27 

•51 
.62 

•39 

.42 
•47 
•35 

•36 

•39 

.27 

.29 

•  31 

.27 

.46 
•  47 
•43 

.08 
.11 
•03 

„          -,                   Average. 

Second                   Greatest. 

Mol^^-            Least. 

.78 

•94 
.62 

.28 
•3t 
•23 

•5r 
.66 

•35 

.26 
•3t 
•23 

•45 
•49 
•39 

•41 
•57 
•31 

•05 
•15 
.00 

TTiird                      Average. 
Tliii^d                      Greatest. 
M°^^^-            Least. 

.67 
.86 

•55 

.24 

•31 
.19 

.44 
•59 
•31 

•33 
•43 
•27 

•23 
•31 
•  19 

.02 
.09 
.00 

MEASUREMENTS   OF   THE   TEETH. 


19 


LOWER  TEETH. 


Table  of  Measurements  of 
THE    Teeth    of    Man;    in 
Inches  and  Hundredths 
OF  AN  Inch. 

'c3 

O 

a 
^4 

0 

u 

0 

-(-> 

a 
<u 
h4 

0 
0 
u 

a 

tn  ■^-l 

CJ 

i5  n 

tn  i^ 

6  ^ 

CJ  <u 
.Q  be 

-56 
0  •.::3 

a  > 

>  n 
3  bo 

LOWER  TEETH. 

a 

Central                  Average 
Incisor.          Greatest. 
Least. 

.80 
•94 
•63 

•34 
.41 
.27 

•47 
.62 

•35 

.2  2 

2  J 

•19 

•13 
•  19 
.09 

•23 
.26 
.21 

.09 
.11 
•05 

Lateral                   Average 
Incisor.          Greatest. 
Least. 

•S3 

i.q6 

.70 

•35 
.46 
.27 

.so 
.66 
•43 

•23 
.26 

•19 

•  15 

•  19 

.11 

•25 
.29 

•25 

.09 

•13 
.08 

Average. 
Cuspid.                  Greatest. 
Least. 

1. 01 

1.28 

.78 

.40 
.46 
•32 

.60 
.82 
•43 

•54 
.70 

•43 

.27 

•35 
•23 

•20    .31 

•27  1  .39 
.11    .24 

.11 
.14 
.08 

First                       Average 

.84 

1.02 

•71 

•30 
•35 
•  25 

.27 
•32 
•23 

.18    .30 

.20      .3[ 
.16      .27 

[ 

•03 
•05 
.01 

Second                   Average 
Bicuspid.       gj2t 

.87 

1.02 

.71 

•31 

•43 
•23 

•56 
•63 
•45 

.28 
•32 
•25 

.18  '.31 
•25      .35 
•15     .27 

.02 
.07 
.00 

First                       Average. 
Molar.            Greatest. 
Least. 

.78 
•94 
•71 

•30 
•39 

.27 

•52 

•59 
•43 

■3? 
•37 
•23 

•33      ^40 
•37      ^45 
•29      ^39 

.04 
.07 
.00 

Second                   Average 
Molar.            Greatest. 
Least. 

.78 
.86 
•71 

.27 
•3t 
•23 

•50 
•55 
•47 

•42 
•45 
•39 

•32   '  .39 

•33    :    -41 

•31   1  .37 

1 

.00 
.00 
.00 

Third                   *^"f8";- 
Mo,ar.           g-;-,. 

.72 
.78 
•63 

.26 
•32 
•23 

.36 
.66 
•31 

.42 

•47 
•31 

•  32 

•37     : 

.20  ' 

•38 
.41 

•35 

.00 
.04 
.00 

20 


MEASUREMENTS    OF    THE    TEETH. 


UPPER  AND   LOWER 

TEE 

TH. 

Table  of  Measurements  oe 
THE  Deciduous  Teeth  of 
Man,  Given  in  Inches  and 
Hundredths  of  an  Inch. 

u 

% 

"So 
a 

0 

0 

M 

s 

3 

Length  of  root. 

Mesio-distal 
diameter  of  crown. 

u 

'O  0 

.ii  a; 
tn  -u 

Labio  lingual 
diameter  of  crown. 

•S  0 
"a  ^ 

0    (U 

Average  only. 

51 

UPPER  TEETH. 

'C 

Central  Incisors. 

•63 

•23 

•39 

•25 

.18 

.20 
•19 

.16 

Lateral  Incisors. 

.62 

.74 

•59 

.68 

•55 

•25 

•45 

.20 

.14 

.14 

Cuspid. 

•25 
.20 
.22 

.19 

•53 

.27 

.20 

.27 

.21 

First  Molar. 

•39 

.46 

.35 

.28 

.20 

•33 

.27 

Second  Molar. 

•32 
•15 

•25 
.11 

•39 
•  15 

•32 

LOWER  TEETH. 

Central  Incisor. 

•13 

Lateral  Incisor. 

•59 

.19 

•39 

•15 

.11 

•15 

•17 

•13 

Cuspid. 

.66 

•23 

•45 

•19 

.14 

.15 

First  Molar. 

.62 

.62 

•24 

.38 

•30 

•25 

•  27 

.21 

Second  Molar. 

.21 

■  44 

•38 

.28 

•34 

•25 

UPPER  CENTRAL  INCISORS.  21 

UPPER  CENTRAL  INCISORS. 

Note. — Usually,  in  the  descriptions  of  the  teeth,  those  of  one  side  only 
will  be  mentioned,  without  reference  to  which  side  in  the  text.  Accompany- 
ing the  illustrations,  the  side  to  which  the  tooth  belongs  will  be  given.  The 
student  will  readily  determine  to  which  side  a  given  example  belongs  by  com- 
paring it  with  the  text  and  correctly  naming  its  surfaces.  Students  should 
remember  that  the  cuts  are  representations  of  individual  teeth  while  the  text 
describes  the  average  forms,  therefore  the  cuts  will  not  always  exactly  corres- 
pond with  the  text. 

16.  The  right  and  left  upper  central  incisors  are  situ- 
ated in  the  extreme  anterior  part  of  the  dental  arch,  one  on 
each  side  of  the  median  line,  their  mesial  surfaces  proximat- 
ing  each  other.  The  crown  presents  four  surfaces,  four 
angles*  and  a  cutting  edge,  or  incisal  surface.  The  general 
contour  of  the  crown  is  similar  to  a  wedge,  with  rounded 
angles,  and  merging  into  a  rounded  form  at  the  thick  end, 
or  the  neck  of  the  tooth;  It  is  slightly  bent  on  its  shorter 
diameter,  so  as  to  make  the  flattened  labial  surface  convex ; 
while  the  other,  the  lingual,  is  concave.  The  crown  is  also 
slightly  bent  in  the  mesio-distal  direction,  so  that  the  labial 
surface  is  convex  and  the  lingual  concave  in  this  direction. 
Therefore,  there  is  a  general  convexity  of  the  labial,  and  a 
general  concavity  of  the  lingual  surface. 

17.  The  labial  surface  of  the  crown  of  the  upper  central 
incisor  (Fig.  1),  in  its  general  form,  is  an  imperfect  square, 
with  its  gingival  side  rounded.  The  mesial  margin  is  a  little 
longer  than  the  distal,  so  that  the  cutting  edge  slopes  away 
toward  the  disto-incisal  angle  (Fig.  1,  h).  Both  the  angles, 
formed  by  the  proximate  surfaces  and  cutting  edge,  are 
slightly  rounded,  the  disto  incisal  more  than  the  mesio- 
incisal,  after  which  the  proximate  surfaces  converge  toward 
the  long  axis  of  the  tooth,  making  the  crown  a  little  nar- 
rower at  the  neck  than  at  the  cutting;  edffe. 

18.  The  lingual  surface  of  the  crown  (Fig.  2)  is  concave 
in  all  directions,  forming  a  fossa,  bounded  by  the  cutting 
edge  (a),  the  mesial  and  distal  marginal  ridges  (?i,  m)  and 


22  UPPER    CENTRAL    INCISORS. 

the  linguo-gingival  ridge,  or  cingulum  (d).  The  marginal 
ridges  are  strong  elevations  of  the  enamel,  running  from  the 
mesio-incisal  and  disto-incisal  ano-les  alono-  the  borders  of  this 
surface  to  near  the  gingival  line,  where  they  join  the  linguo- 
gingival  ridge.  The  linguo-gingival  ridge  is  a  strong  eleva- 
tion of  the  enamel  forming  the  linguo-gingival  border  of  the 
crown.  It  is  sometimes  elevated  into  a  tubercle.  The  lin- 
gual fossa  is  usually  smooth,  and  the  ridges  by  wdiich  it  is 
bounded  are  not  prominent.  In  many  instances,  however, 
there  is  a  deep  pit  at  the  junction  of  the  linguo-gingival  ridge 
with  the  lingual  surface  proper ;  and  in  some  a  groove  ex- 
tends from  the  pit  for  a  short  distance  along  the  border  of 
each  marginal  ridge  (Fig.  3).  These  latter  may,  or  may  not, 
be  fissured.  In  a  few  examples  the  enamel  of  this  surface 
has  irregular  wrinkles,  or  ridges  and  grooves,  running  from 
the  linguo-gingival  ridge  toward  the  cutting  edge.  In  mal- 
formed teeth  this  surface  is  often  very  imperfect. 

19.  The  mesial  and  distal  surfaces  each  present  the 
outline  of  the  letter  V,  w^ith  its  lines  curved  with  the  con- 
vexity toward  tlie  lips,  and  the  acute  angle  at  the  cutting 
edge  (Fig.  4).  The  mesial  surface  is  almost  straight  from  the 
mesio-incisal  angle  to  the  gingival  line.  It  is  convex  from 
labial  to  lingual,  but  nearly  flat  toward  the  gingival  line : 
Mobile  in  some  there  is  even  a  slight  concavity,  centrally  at, 
or  near,  the  gingival  line.  In  the  labio-lingual  direction, 
the  distal  surface  is  rounded,  as  in  the  mesial.  In  the  ma- 
jority of  examples  it  is  also  convex  in  the  direction  of  the 
long  axis  of  the  tooth,  so  that  it  bellies  out  toward  the  lateral 
incisor. 

20.  At  the  gingival  line,  the  tooth  is  a  little  constricted, 
forming  a  slight  furrow;  or  rather,  the  root  at  the  neck  is 
a  little  smaller  than  the  crown,  and  the  enamel  slopes  down 
to  the  size  of  the  root,  giving  the  appearance  of  a  continuous 
ridge  of  enamel  around  the  neck.  This  line  does  not  run 
horizontally  around  the  neck  of  the  tooth.     On  the  proximate 


§'-^%-'^ 

H 

I'    \^^ 

h) 

e      a.  it    i^ 

Fig.  1. 

u 


J 


^^ 


Fig. 


Fis.  4. 


Fig.  I*  (Par.  17),— Right  Upper  Central  Incisor,  Labial  Surface,  a,  Cutting 
edge  ;  6,  mesial  surface  ;  c,  distal  surface  ;  d,  labial  surface  ;  e,  e,  labial  grooves ;  ^.mesio- 
ineisal  angle  ;  h,  disto-incisal  angle ;  i,  body  of  root ;  /.-,  apex  of  root. 

Fig.  2*  (Par.  18).— Right  Upper  Central  Incisor,  Lingual  Surface.  «,  Cutting 
edge ;  b,  mesial  surface  ;  c,  distal  surface  ;  d,  linguo-gingival  ridge,  or  cingulum ;  /,  gin- 
gival line  ;  g,  mesio-incisal  angle  ;  li,  disto-incisal  angle  ;  i,  body  of  root ;  /.-,  apex  of  root ; 
m,  distal  marginal  ridge ;  n,  mesial  marginal  ridge. 

Fig.  3*  (Par.  18).— Left  Upper  Central  Incisor,  Lingual  Surface,  sbowing  lingual 
pit.  The  cutting  edge,  a,  is  considerably  worn.  The  mesial  and  distal  marginal  ridges,  6, 
c,  are  prominent ;  cl,  linguo-gingival  ridge ;  /,  gingival  line ;  g,  mesio-incisal  angle ;  h, 
disto-incisal  angle  ;  i,  body  of  root ;  k,  apex  of  root ;  m,  lingual  pit. 

Fig.  4*  (Par.  19).— Right  Upper  Central  Incisor,  Mesial  Surface,  a,  Mesio-incisal 
angle ;  d,  linguo-gingival  ridge ;  /,  /,  gingival  line,  showing  its  labio-lingTial  curvature  ; 
i,  body  of  root ;  k,  apex  of  root. 

Fig.  5*  (Par.  21).— Left  Upper  Central  Incisor,  Lingual  Surface.  Young,  un- 
worn tooth.  The  developmental  lines,  or  grooves,  are  made  diagrammatically  promi- 
nent to  show  the  form  ot  the  lobes,  a,  Middle  lobe;  h,  mesial  lobe  ;  c,  distal  lobe ;  d, 
lingual  lobe ;  c,  e,  linguo-gingival  groove  ;  /,  /,  lingual  developmental  grooves ;  g,  mesio- 
incisal  angle  ;  h,  disto-incisal  angle. 


*  Illustration,  13^  diameters. 


UPPER   CENTRAL  INCISORS.  25 

sides  it  forms  curves  with  the  convexity  toward  the  crown, 
that  on  the  mesial  being  a  little  the  greater,  and  on  the 
labial  and  lingual  surfaces  it  forms  a  curve  with  the  con- 
cavity toward  the  crown.  This  line  marks  the  limit  of  the 
attachment  of  the  peridental  membrane  and  gum  tissue  to 
the  root  of  the  tooth. 

21.  Developmental  lines  (Fig.  5).  "When  any  of  the 
incisors  first  appear  through  the  gums  there  are  three  little 
eminences,  or  tubercles,  called  mammelons,  on  the  cutting 
edge  with  grooves  crossing  from  labial  to  lingual  between 
them  (a,^,  h).  These  grooves  run  some  distance  on  the  labial 
surface,  becoming  broader  and  shallower  till  they  disappear. 
In  many,  these  lines  appear  on  the  lingual  surface  between 
the  marginal  ridges  and  the  fossa  (/,/).  Occasionally,  they 
are  seen  as  far  as  the  linguo-gingival  ridge.  The  mammelons 
are  soon  removed  from  the  edge  by  wear,  leaving  it  straight, 
or  slightly  curved.  These  lines  divide  this  part  of  the  crown 
of  the  tooth  into  three  labial  lobes.  Calcification  begins  in 
these  mammelons  as  separate  pieces,  or  plates,  and  the  grooves 
are  the  marks  of  the  after-coniiuence  of  these  plates.  This  is 
common  to  the  incisors  and  cuspids.  These  teeth  are  some- 
times fissured  across  the  cutting  edge,  marking  an  imperfect 
confluence  of  the  primary  plates.  The  calcification  of  the 
linguo-gingival  ridge,  or  cingulum,  is  also  begun  as  a  sepa- 
rate plate,  forming  the  lingual  lobe,  but  afterward  it  becomes 
united  to  the  other  parts  by  confluence,  leaving  a  groove, 
often  very  slight,  indeed,  and  soon  obliterated  by  wear, 
marking  the  line  of  union.  This  is  the  linguo-gingival 
groove  (e,  e).  (This  groove  is  properly  three  grooves  corres- 
ponding with  the  mesial,  central,  and  distal  grooves  of  the 
bicuspids,  while  the  linguo-gingival  ridge  corresponds  to  the 
lingual  cusp.  See  Par.  41.)  In  smooth  regularly  formed 
teeth  it  begins  at  the  gingival  line  just  lingual  of  the 
summit  of  its  labio-lingual  curvature,  and  runs  across 
the  maro;inal  rido;e  at  rio-ht  ano-les  with  its  lensrth,  then  runs 


26  UPPER    LATERAL    INCISOR. 

almost  horizontally  across  the  lingual  surface  to  the  distal 
marginal  ridge.  This  ridge  is  now  crossed  at  right  angles, 
and  the  gingival  line  reached.  The  length  of  the  groove 
usually  includes  from  a  quarter  to  a  third  of  the  circumfer- 
ence of  the  tooth.  When  the  linguo-gingival  ridge  is  ji^romi- 
nent,  or  rises  in  the  form  of  a  tubercle,  this  groove  is  subject 
to  much  variation  in  its  course.  Often,  there  is  a  deep  pit 
in  the  center  of  its  length;  i.  e.,  centrally  in  the  lingual  sur- 
face, at  the  margin  of  the  linguo-gingival  ridge  "(Fig.  3,  in). 
From  this,  fissures  may  extend  laterally.  Occasionally,  espe- 
cially in  the  lateral  incisors,  a  sulcus,  or  a  fissure  divides  the 
linguo-gingival  ridge  from  one  of  the  marginal  ridges,  and 
extends  into  the  cementum  (Fig.  10).  This  is  the  linguo- 
gingival  fissure. 

22.  The  root  of  the  upper  central  incisor  (Figs.  1  to  5) 
is  about  one  and  a  fgurth,  to  one  and  a  half  times  as  long  as 
the  crown.  It  is  conical  in  form,  tapering  from  the  crown 
to  the  apex ;  less  rapidly  near  the  neck,  and  more  rapidly  as 
the  apex  is  approached.  Therefore,  the  body  of  the  root 
seems  a  little  swollen.  However,  the  root  of  this  tooth 
presents  great  variety  of  figure,  as  do  the  roots  of  teeth 
generally.  The  root  is  nearly  round  at  the  neck.  The  cur- 
vature of  the  lingual  surface  is  the  arc  of  a  smaller  circle 
than  that  of  the  labial.  The  proximate  surfaces  are  slightly 
flattened.  The  flattened  portion  of  the  mesial  surface  is  a 
little  broader  than  the  distal.  These  two  convero;e  to  the 
lingual,  giving  the  form  of  a  prism  with  its  angles  rounded. 

UPPER   LATERAL   INCISOR. 

23.  The  description  of  the  lateral  incisor  maybe  much 
abridged,  because  of  its  resemblance  to  the  central  in  its 
general  form  and  developmental  lines.  The  tooth  is  a  little 
shorter,  and  from  mesial  to  distal  the  crown  is  about  a  third 
narrower. 

24.  The  labial  surface  of  the  lateral  incisor  (Fig.  6)  is 


Fl?    7. 


r-A 


Fig.  6*  (Par.  24).— Right  Upper  Latehxl  Incisor,  Labial  Surface,  a,  Cutting 
edge;  c,  distal  surface;  e,  labial  grooves;  /,  gingival  line;  g,  mesio-incisal  angle;  /(, 
disto-incisal  angle. 

Fig.  7*  (Par.  25).— Right  Upper  Lateral  Incisor,  Mesial  Surface,  a,  Me'sio-incisal 
angle ;  d,  linguo-gingival  ridt;e ;  /,  /,  gingival  line  ;  i,  body  of  root ;  /;,  apex  of  root. 

Fig.  8*  (Par.  26;.- Right  Upper  Later.a.l  Incisor,  Lingt'al  Surface,  without  lingual 
pit.  a.  Cutting  edge ;  b.  mesial  marginal  ridge ;  c,  distal  marginal  ridge ;  d,  linguo- 
gingival  ridge  ;  /,  gingival  line  ;  g,  mesio-incisal  angle ;  h,  disto-incisal  angle ;  i,  body  of 
root ;  k,  apex  of  root ;  m,  lingual  fossa. 

Fig.  9*  (Par.  2G).— Right  Upper  Lateral  Incisor,  Lingual  Surface,  Avith  lingual 
pit.  a,  Cutting  edge  ;  b,  mesial  marginal  ridge ;  c,  distal  marginal  ridge,  with  linguo- 
gingival  groove  crossing  it ;  d,  linguo-gingival  ridge,  or  cingulum  ;  /,  gingival  line ;  ;/, 
mesio-incisal  angle ;  h,  disto-incisal  angle ;  i,  body  of  root ;  I:,  apex  of  root ;  m,  lingual 

pit. 

Fig.  10*  (Par.  26).— Eight  upper  Lateral  Incisor,  showing  a  linguo-gingival  fissure. 
CI,  Cutting  edge ;  b,  linguo-gingival  groove  fissured ;  /,  gingival  line ;  g,  mesio-incisal 
angle ;  /(,  disto-incisal  angle. 

Fig.  11*  (Par.  27).— Upper  Lateral  Incisor,  Mesial  Surface.  Very  short  root,  a, 
mesio-incisal  angle  ;  d,  linguo-gingival  ridge ;  /,  g  ngival  line. 

♦Illustration,  IJ^  diameteis. 


UPPER   LATERAL   INCISOR.  29 

more  rounded  in  the  mesio-distal  direction  than  in  the  cen- 
tral. The  mesio-incisal  angle  is  acute,  and  the  cutting  edge 
slopes  away  in  a  curve  to  a  rounded  and  obtuse  disto-incisal 
angle.  The  cutting  edge,  at  the  time  of  eruption,  presents 
three  tubercles,  or  mammelons,  and  the  grooves  crossing  the 
edge  between  these  are  projected  on  the  labial  surface  as 
shallow  labial  grooves. 

25.  The  mesial  (Fig.  7)  and  distal  surfaces  present  the 
characteristic  V-shape  of  all  the  incisors.  From  labial  to 
lingual  the  mesial  surface  is  rounded  near  the  cutting  edge, 
but  much  flattened  near  the  gingival  line.  Sometimes  a 
slight  concavity  exists  at  this  point.  Occasionally  the  mesio- 
labial  angle  has  a  flattened  or  sunken  point  of  enamel  near 
the  middle  of  its  length.  This  is  sometimes  broad  and  of 
notable  depth,  and  in  this  case  is  generally  in  the  labial 
portion  of  the  mesial  surface.  In  others,  it  is  a  small  im- 
perfection in  the  mesial  margin  of  the  labial  surface.  The 
distal  surface  is  convex  in  all  directions.  In  its  incisal  third, 
it  rounds  out  freely  toward  the  cuspid,  but  becomes  more 
flattened  toward  the  gingival  line. 

26.  The  lingual  surface  (Fig.  8)  of  lateral  incisors,  is 
very  irregular  in  the  extent  of  its  concavity.  Some  are 
almost  flat,  while  others  are  deeply  concave.  The  mesial 
and  distal  marginal  ridges  are  proportionately  broader  and 
stronger  than  in  the  centrals.  In  the  majority  of  examples 
the  lingual  surface  is  the  broadest  part  of  the  crown.  The 
rounding  of  the  proximate  surfaces  is  at  the  expense  of  the 
labial  surface,  so  that  a  moderately  acute  angle  is  formed  by 
the  junction  of  the  proximate  surfaces  with  the  lingual. 
Generally,  the  lingual  surface  is  almost  smooth,  but  in  many, 
a  pit,  with  or  without  lateral  fissures,  will  be  found  at  the 
junction  of  the  lingual  surface  proper,  with  the  linguo-gin- 
gival  ridge  (Fig.  9).  In  some  of  these,  the  linguo-gingival 
ridge  is  unusually  short,  so  that  the  marginal  ridges  are  folded 
in  together  at  their  gingival  ends,  forming  a  deep  sulcus 


30  THE    LOAVER    I^'CISORS. 

between  them,  and  there  is  a  deep  pit  at  their  junction.  Again, 
some  are  found  in  which  there  is  a  deep  groove,  which  is 
often  fissured,  dividing  one  marginal  ridge  from  the  linguo- 
gingival  ridge,  and  extending  into  the  cementum  (Fig.  10), 
This  is  sometimes  nearly  central,  giving  the  appearance  of  a 
failure  of  the  lingual  lobe,  or  of  a  division  of  the  lobe  cen- 
trally, or  of  the  displacement  of  the  lobe  to  one  side.  This 
is  the  linguo-gingival  fissure. 

27.  The  root  of  the  upper  lateral  incisor  (Figs.  6  to  11) 
is  conical,  but  considerably  flattened  on  its  mesial  and  distal 
sides,  which  is  generally  maintained  to  the  apex.  The  root 
is  generally  straight,  and  about  one  and  a  half  times  as  long 
as  the  crown.  In  many  specimens  the  apex  is  curved  to  the 
distal.     Occasionally  the  root  is  very  crooked. 

28.  The  upper  lateral  incisor  presents  much  variety  of 
size  and  form.  It  is  not  uncommon  to  find  narrow  laterals 
associated  with  broad  centrals.  The  lateral  upper  incisors 
are  more  often  wanting,  or  imperfectly  developed,  than  the 
other  anterior  teeth.  In  the  latter,  the  crown  of  the  tooth 
is  frequently  conical,  with  a  rounded,  or  even  a  moderately 
sharp,  point. 

THE    LOAYER    INCISORS. 

29.  The  lower  incisors  have  outlines  similar  to  the 
upper  lateral,  but  are,  in  every  way,  more  slender.  Their 
developmental  lines  are  the  same,  but  the  grooves  are  much 
less  marked,  and  generally  cannot  be  seen  except  in  unworn 
teeth.  The  cutting  edge  of  the  lower  central  (Fig.  12)  is 
very  nearly  at  right  angles  with  the  long  axis  of  the  tooth, 
and  its  mesio-  and  disto-incisal  angles  are  square  and  sharp. 
From  mesial  to  distal,  the  cutting  edge  is  the  widest  part  of 
the  crown,  and  from  it  the  proximate  surfaces  converge 
equally  to  the  gingival  line,  reducing  the  mesio-distal  diam- 
eter about  a  third.  The  lower  lateral  differs  from  the  central 
by  the  cutting  edge  sloping  away  to  the  distal,  the  mesio- 
incisal  angle  being  acute,  and  the  disto-incisal  angle  obtuse  and 


Fis.  12. 


Fig.  15. 


Fig.  17. 


Fig.  12*  (Par.  29).— Left  Lower  Central  Incisor,  Labial  Surface./  Long  root,  a. 
Cutting  edge  ;  e,  labial  grooves  ;  /,  gingival  line  ;  g,  mesio-incisal  anglp  ;  Zi.'disto-incisal 
angle. 

Fig.  13*  (Par.  29).— Left  Lower  Lateral  Incisor,  Labi.il  Surface.  Long  root,  a. 
Cutting  edge ;  e,  labial  grooves ;  /,  gingival  line  ;  g,  mesio-incisal  angle  ;  Ji,  disto-ineisal 
angle  ;  i,  body  of  root ;  k.,  apex  of  root. 

Fig.  14*  (Par.  29).— Right  Lower  Lateral  Incisor,  Labial  Surface.  Short  root. 
a,  Cutting  edge ;  e,  labial  grooves ;  /,  gingival  line ;  g,  mesio-incisal  angle ;  h,  disto- 
ineisal  angle ;  i,  body  of  root ;  k,  apex  of  root. 

Fig.  15*  (Par.  30).— Lower  Central  Incisor,  Lingual  Surface,  a,  Cutting  edge ; 
*,  mesial  marginal  ridge;  c,  distal  marginal  ridge;  d,  linguo- gingival  ridge;  g,  mesio- 
incisal  angle  ;  h.  disto-ineisal  angle  ;  m,  lingual  ridge. 

Fig.  16*  (Par.  30).— Lower  Central  Incisor,  Distal  Surface,  a.  Cutting  edge ;  the 
edge  is  worn  away  as  represented  by  the  line ;  d,  linguo-gingival  ridge ;  /,  /,  gingival 
line ;  i,  groove  along  the  distal  side  of  root ;  k,  apex  of  root. 

Fig.  17*  (Par.  31).— Right  Lower  Lateral  Incisor,  Distal  Surface,  showing  root 
deeply  grooved,  a.  Cutting  edge ;  d,  linguo-gingival  ridge ;  /,  gingival  line  ;  i,  deep  groove 
in  root ;  k,  apex  of  root. 

*  Illustration,  IJ^  diameters. 


THE    CUSPIDS.  33 


rounded.     The  distal  surface  is  also  convex  from  the  disto-inci- 
sal  angle  to  the  gingival  line,  bellying  out  toward  the  cuspid* 

30.  The  lingual  surface  (Fig.  15)  of  the  lower  incisors 
is  concave  from  the  cutting  edge  to  the  linguo-gingival  rido-e, 
over  which  there  is  a  convexity  (Fig.  16).    :N'ear  the  cutting 

•  edge  this  surface  is  generally  nearly  flat  in  the  mesio-distal 
direction,  but  is  sometimes  concave  or  slightly  convex  ;  it 
becomes  convex  progressively  toward  the  linguo-gingival 
ridge.  In  many  there  is  a  slight  ridge  on  the  center  of  this 
surface  with  a  shallow  concavity  on  either  side,  which  marks 
the  junction  of  the  lobes,  running  from  near  the  cutting-edge 
to  the  linguo-gingival  ridge  (Fig.  15).  The  mesial  and 
distal  surfaces  are  convex  near  the  cutting  edges,  but  become 
flattened,  and  sometimes  slightly  concave,  toward  the  o-in- 
gival  line. 

31.  The  roots  of  the  lower  incisors  are  slender  and  much 
flattened  in  their  mesio-distal  diameter,  and  not  unfrequently 
slii^htly  grooved  on  the  mesial  and  distal  sides.  While  the 
flattening  of  the  crown  of  the  low^er  central  is  generally  at 
right  angles  with  the  flattening  of  its  root,  the  distal  portion 
of  the  crown  of  the  lower  lateral  is  directed  more  to  the 
lingual,  so  as  to  appear  slightly  twisted  on  its  root  in  most 
examples.  The  labial  surface  of  the  crown  and  root,  in  its 
length,  forms  nearly  the  arc  of  a  circle  (Fig. -17),  though  the 
curve  of  the  surface  of  the  crown  is  usually  a  little  greater 
than  that  of  the  root  (Fig  16).  The  lingual  surface  of  the 
root  is  almost  straight,  but  in  the  apical  third  it  is  convex, 
sloping  away  to  form  the  apex.  The  roots  of  these  teeth 
are  generally  straight,  but  occasionally  the  apex  is  curved  to 
the  distal. 

THE    CUSPIDS. 

32.  We  have  four  cuspids,  one  on  each  side  in  the 
upper,  and  one  on  each  side  of  the  lower  jaw.  They  are 
sometimes  called  canine  teeth,  or  eye  teeth.  They  are  situated 
at  the  angles  of  the  mouth,  between  .the  lateral  incisors. 


D 


S4  THE   UPPER   CUSPID. 


and  the  first  bicuspids.  They  are  tliird  from  the  median 
line,  and  are  large,  and  strong  teeth  of  simple  form,  firmly 
implanted  in  the  alveolar  process  by  a  long,  strong  root. 

THE    UPPER    CUSPID. 

33.  The  labial  surface  of  the  crown  of  the  upper  cuspid 
(Fig.  18)  is  a  little  narrower  in  the  mesio-distal  direction 
than  in  the  central  incisor,  with  nearly  equal  length  from 
the  point  of  the  cusp  to  the  gingival  line.  Instead  of  a 
straight,  or  onl^^  slightly  curved  cutting  edge,  as  in  the  in- 
cisors, the  central  portion  of  the  crowni  is  extended  into  a 
well-formed  point  («),  W' ith  cutting  edges  sloping  away  to  the 
mesio-incisal  and  disto-incisal  angles  (^,  h).  Of  these  cutting 
•edges,  the  distal  is  a  little  the  longer,  and  from  the  disto- 
incisal  angle  to  the  gingival  line,  the  distal  surface  is  a  little 
■shorter  than  the  mesial.  In  unworn  teeth,  tlie  angle  formed 
by  the  union  of  the  cutting  edges  to  form  the  cusp  is  usually 
about  ninety  degrees,  or  a  square.  The  point  is  a  little  rounded 
at  first,  but  is  soon  much  rounded  or  flattened  by  wear.  Both 
the  mesial  and  distal  margins  of  the  labial  surface  of  the 
crown,  from  the  mesio-  and  disto-incisal  angles  to  the  gingival 
line,  slope  toward  the  central  axis  of  the  tooth, — the  distal 
slope  being  the  greater.  This  narrows  the  crown  at  the  neck 
nearly  one-third  from  the  width  of  its  widest  point.  The 
curvature  of  the  gingival  line  on  this  surface,  marking  the 
termination  of  the  crown,  is  about  a  quarter  circle.  The 
surface  is  convex  in  all  directions,  and  is  much  more  rounded 
in  the  mesio-distal  direction  than  in  the  incisors.  In  the 
direction  of  its  length,  the  convexity  is  about  the  same  as  in 
the  incisors.  The  greater  convexity  mesio-distally  is  caused 
by  a  strong  labial  ridge  {d)  running  from  the  point  of  the 
cusp  to  the  gingival  line.  This  ridge  occupies  so  much  of 
the  surface  of  the  tooth  that  its  margins  are  imperfectly  de- 
fined. It  belongs  to  the  middle  lobe,  developed  from  the 
middle  plate,  which,  in  the  incisors,  is  the  smallest  of  the 


fs   It 


Fig.  is*  (Par.  33).— Right  Upper  Cuspid,  Labial  Surface,  a,  Point  of  ciisp ;  d,  labial 
Tidge;  e,  labial  grooves;  ,/',  gingival  lm(j;  g,  mesiQ.-incisal  angle;  h,  disto-iircisal  angle 
i,  body  of  loot ;  /.-,  apex  of  root.    '*^  \  ft'-<^»»t/  rui-^  • 

Fig.  19^  (Par.  31).— PasHX  Upper  Cuspid,  Lingual  Sdef-^ce.  The  more  common 
form,  a,  Point  of  cusp ;  d,  linguo-gingival  ridge  ;  f ,  e,  lingual  grooves  :  /",  gingival  line  ; 
g,  mesio-iacisal  angle  :  h,  disto-incisal  angle  :  /,  body  of  root ;  /.-,  apes  of  root ;  m,  lino-ual 
ridge. 

Fig.  20*  (Par.  34).— Eight  LTpper  Cuspid,  Lingual  Surface  of  irregular  form,  a, 
Point  of  cusp  ;  d,  linguo-gingival  ridge  ;  c,  e,  lingual  grooves  ;  j\  gingival  line  ;  g,  mesio- 
incisal  angle  ;  h,  disto-iucisal  angle;  m,  prominent  lingual  ridge  ;  ;;,  two  small  tubercles 
on  linguo-gingival  ridge. 

Fig.  21*  (Par 3.5). —Right  Upper  Cuspid,  Mesial  Surf.\ce.  a,  Point  of  cusp;  6, 
mesial  marginal  ridge ;  c,  point  of  slight  concavity  of  mesial  surface  ;  d.  linguo-gingival 
ridge :  c ,  labial  groove ;  /,  /,  gingival  line  ;  g,  mesio-incisal  angle  ;  /,  body  of  root ;  k, 
apex  of  root. 

Fig.  22*  (Par.  37).— Left  Upper  Cuspid,  with  a  very  long  and  crooked  root. 

Fig.  23*  (Par.  37).— Right  Upper  Cuspid,  with  a  peculiarly  crooked  root. 

Fig.  2-1*  (Par.  37).— Left  Upper  Cuspid,  with  a  very  small  and  short  roi>t. 

*  Illustration,  1^  diameters 


THE    UPPER    CUSPID. 


37 


three,  but  in  this  tooth  is  much  the  largest".  There  are  two 
Labial  furrows  (e),  or  a  flattening  of  the  convexity  between 
the  central  line  of  the  ridge  and  each  angle,  marking  the 
junction  of  the  lobes.  These  i'urrows  are  usually  lost  by 
becoming  shallower  before  reaching  the  center  of  tbe  length 
of  the  crown.  In  well-formed  teeth,  this  surface  presents  a 
uniform  enamel,  free  from  pits  or  sulci. 

34.     The  lingual  surface  (Fig.  19)  presents  the  same 
general  marginal  configuration  as  the  buccal,  though  it  is 
somewhat  narrower  toward  the  gingival  line.     This  is  caused 
by  the  arc  of  convexity  of  the  lingual  surface  of  the  neck  of 
the  tooth  being  of  a  smaller  circle  than  that  of  the  buccal, 
and  by  the  flattening  of  the  proximate  surfaces  on  lines  which 
converge   rapidly  to  the  lingual.     This   surface  is  usually 
almost  straight  from  the  cusp  to  the  linguo-gingival  ridge, 
or  cingulum,  but  is  sometimes  slightly  concave.    The  linguo- 
gingival  ridge  is  sharply  convex  and  longer  from  the  gingival 
line  to  the  point  of  convexity  than  in  the  incisors.     (Fig. 
21,  d.)     Mesio-distally  this  surface  is  slightly  convex  in  its 
central  part  on  account  of  the  lingual  ridge  which  runs  from 
the  point  of  the  cusp  nearly,  or  quite,  to  the  cingulum.     On 
each  side  of  this,  and  between  it  and  the  marginal  ridges, 
there   is   a  slight   but  well-defined   concavity  and   furrow, 
marking  the  confluence  of  the  lobes.     The  marginal  ridges. 
arise  from  the  mesio-  and  disto-incisal  angles  and  unite  with 
the   linguo-gingival  ridge  or  cingulum.     These   ridges  are 
usually  large  near  the  angles,  and  much  less  pronounced 
toward  the  linguo-gingival  ridge.     The  latter  is  prominent, 
and  is  ofteii  raised  into  a  tubercle,  or  slight  cusp.     Occasion- 
ally this  part  of  the  enamel  is  thrown  into  irregular  folds, 
with  grooves  between,  which  are  sometimes  fissured.     More 
rarely^he  small  cusp  may  be  divided  by  a  groove  (Fig.  20,  n). 
.The  linguo-gingival  groove  is  often  pronounced  in  unworn 

1»cth. 

35.     The  mesial  surface,  near  the  incisal  angle  (Fig. 


38  THE    LOWER    CUSPIDS. 

21),  is  convex  in  all  directions,  but  becomes  flattened,  and 
occasionally  slightly  concave,  near  the  gingival  line  (c). 

36.  The  distal  surface  is  similar  to  the  mesial,  but  is 
more  convex,  usually  being  well  rounded  in  the  labio-lingual 
direction  to  the  ffing-ival  line.  But  in  the  direction  of  the 
long  axis  of  the  tooth  this  surface,  on  account  of  its  distal 
projection  is  first  convex,  and  further  toward  the  gingival  line 
is  concave,  especially  near,  and  at  the  neck  of  the  tooth.  The 
labio-lingual  curvature  of  the  gingival  line  is  about  2.5  m.m., 
varying  from  1.0  m.m.  to  3.5  m.m.  on  the  mesial  surface^ 
and  a  little  less  on  the  distal. 

37.  The  root  of  the  upper  cuspid  is  the  longest  in  the 
human  mouth,  averaging,  according  to  my  measurements^ 
17.5  m.m.,  and  varying  from  11.0  to  21.0  from  the  apex  to 
the  gingival  line  at  the  labial  surface.  It  is  irregularly 
conical  in  form,  tapering  from  the  neck  to  the  apex.  Its 
labio-lingual  diameter  is  a  little  greater  than  its  mesio-distal, 
which  gives  the  root  a  flattened  appearance,  but  it  is  seldom 
entirely  flat  on  either  the  mesial  or  distal  surface.  In  most 
examples  the  bod}^  of  the  root  is  straight,  aj)d  tapers  to  a 
slender  point,  which  is  often  curved  to  the  labial  and  distal, 
though  the  form  of  this  root  presents  great  variations.  Fre- 
quently,  it  is  very  crooked,  perhaps,  because,  when  it  is  taking 
its  place  in  the  arch,  it  is  often  crowded  by  the  teeth  mesial 
and  distal  to  it,  so  that  its  growth  in  a  right  line  is  inter- 
rupted.    (See  Figs.  22,  23  and  24.) 

THE  LOWER  CUSPIDS. 

38.  In  their  general  figure,  the  lower  cuspids'  so  closely 
resemble  the  upper,  a  description  of  their  difterences  will  be 
sufiicient.  They  are  slightly  smaller  than  the  upper  cuspids, 
and  the  crowns  are  a  little  longer,  which  make  them  appear 
more  slender.  The  mesial  surface  of  these  teeth  is  usually 
nearly  straight  the  entire  length  of  the  root  and  crown  (Figs. 
25  and  26) ;  so  that  the  increased  width  of  the  crown  over 


Fig,  25. 


Fig.  29. 


Fig.  25*  (Par.  38).— Left  Lower  Cuspid,  Labial  Surface,  a,  Point  of  cusp ;  &,  me- 
sial surface  ;  c,  distal  surface  ;  rt,  labial  ridge ;  e,  distal  labial  groove  ;  /,  gingival  line ;  fir, 
mesio-incisal  angle  ;  h,  disto-incisal  angle  ;  i,  body  of  root ;  k,  apex  of  root. 

Fig.  26*  (Par.  38).— Left  Lower  Cuspid,  Mesial  Surface,  a,  Point  of  cusp;  d,  Im- 
guo-gingival  ridge ;  /,  gingival  line ;  g,  mesio-incsal  angle ;  /,  body  of  root,  which  is 
distinctlv  flattened  ;  k,  apex  of  root. 

Fig.  27*  (Par.  38).— Left  Lower  Cuspid,  Distal  Surface,  a,  Point  of  cusp  ;  c,  labial 
groove ';  'd,  linguo-gingival  ridge ;  e,  concavity  of  the  distal  cutting  edge  where  the 
groove  passes  over  it ;  /,  gingival  line  ;  h,  disto-incisal  angle ;  ;,  body  of  root ;  k,  apex  of 
root. 

Fig.  28*  (Par.  39).— Left  Lower  Cuspid,  Lingual  Surface,  o,  Point  ot  cusp ;  a, 
linguo-gingival  ridge;  e,  lingual  grooves;  /,  gingival  line;  fir,  mesic-incisal  angle;  h, 
disto-incisal  angle ;  i,  body  of  root ;  k,  apex  of  root ;  I,  distal  marginal  ridge ;  m,  lingual 
or  triangular  ridge  ;  n,  mesial  marginal  ridge. 

Fig.  29*  (Par." 40).— Right  Lower  Cuspid,  Mesial  Surface,  a,  Point  of  cusp;  d, 
linguo-gingival  ridge ;  /,  gingival  line ;  fir,  mesio-incisal  angle.  The  root  is  short  auA 
thick. 

*  Illustration,  1%,  diameters. 


THE    BICUSPIDS.  41 


the  root  is  mainly  on  the  distal.  This  causes  a  marked 
prominence  of  the  disto-incisal  angle.  In  many  examples 
this  gives  the  tooth  the  appearance  of  being  bent,  with  a  con- 
siderable concavity  on  the  distal  side  in  the  cervical  region. 
In  young,  unworn  teeth,  the  cusp  is  rather  more  prominent 
and  pointed  than  in  the  upper  cuspid,  and  the  distal  cutting 
edge  is  proportionately  longer ;  but,  as  the  point  of  the  cusp 
comes  directly  in  occlusion  with  the  upper  teeth,  it  is  soon 
worn  to  a  blunt  point,  or  a  flat  surface,  inclining  to  the  labial 
and  sloping  away  to  the  distal. 

39.  The  lingual  surface  (Fig.  28)  is  very  smooth,  and 
the  ridges  are  less  prominent  than  in  the  upper  cuspid.  A 
tubercle  on  the  linguo-gingival  ridge  is  rare.  The  develop- 
mental lines,  or  grooves,  are  the  same  as  those  of  the  upper 
cuspids,  but  less  prominent.  Yet,  generally,  they  can  be 
seen  in  unworn  teeth.  Fissures  are  seldom  seen  in  any  part 
of  this  tooth. 

40.  The  root  of  the  lower  cuspid  (Figs.  25  to  29)  is 
shorter  than  the  upper,  and  generally  more  flattened  in  the 
mesio-distal  diameter,  often  presenting  deep  furrows.  In 
rare  instances,  there  is  a  division  of  the  root  near  ihe  ex- 
tremity. The  root  is  nearly  straight,  and  in  many  examples 
the  lingual  surface  of  the  root  is  nearly  a  straight  line,  while 
the  labial  surface,  root,  and  crown,  present  a  nearly  regular 
convexity.  The  root  is  not  so  often  abnormally  crooked  as 
that  of  the  upper  cuspid,  though,  like  the  upper,  it  is  much 
inclined  to  end  in  a  slender  apex ;  which  is  often  slightly 
bent  in  the  labial  direction. 

THE  BICUSPIDS. 

41.  There  are  eight  bicuspids,  or  premolars,  two  on  each 
side  in  the  upper  jaw,  and  two  on  each  side  in  the  lower  jaw. 
Hence  they  are  called  the  first  and  second  bicuspids.  They 
are  situated  between  the  cuspids  and  first  molars,  and  are 
the   fourth   and   fifth    teeth*   I'rom   the   median    line.     The 


42  UPPER    FIRST    BICUSPID. 

bicuspids,  though  unlike  the  incisors  and  cuspids  in  the  con- 
tour of  their  crowns,  have  the  same  number,  and  a  similar 
distribution  of  primarj^  parts,  or  lobes.  They  are,  indeed, 
formed  on  the  same  general  plan.  The  change  of  form  is 
the  result  of  a  diiferent  relative  development  of  the  parts, 
by  which  the  cinguium,  or  linguo-gingival  ridge,  is  elevated 
into  a  powerful  lingual  cusp ;  which,  in  the  upper  bicuspids, 
is  almost  or  quite  as  high  as  the  buccal  cusp,  but  in  the  lower 
bicuspids,  especiall}^  in  the  first,  is  less  prominent.  The 
middle  lobe  also  forms  a  relatively  larger  part  of  the  buccal 
portion  of  the  crown  than  in  the  incisors  and  cuspids  ;  while 
the  mesial  and  distal,  lobes  are  relatively  smaller.  By  the 
development  of  the  lingual  cusp  of  the  upper  bicuspids,  the 
linguo-gingival  grooves  of  the  incisors  and  cuspids  {q.  v.  21) 
is  carried  to  the  central  part  of  the  crown,  which  it  traverses 
from  mesial  to  distal  in  a  deep  sulcus  (Fig.  30).  It  is  natu- 
rally divided,  by  the  mesial  and  distal  pits  found  at  its 
junction  with  the  triangular  grooves,  into  three  parts :  mesial 
(o),  central  {l\  and  distal  {p).  In  the  lower  bicuspids  the 
lingual  lobe  is  often  very  small  and  the  course  of  the  grooves 
irregular. 

UPPER    FIRST    BICUSPID. 

42.  The  outline  of  the  occlusal  surface  of  the  upper 
first  bicuspid  (Fig.  30),  when  seen  in  a  line  Avith  the  long 
axis  of  the  tooth  is  irregularly  quadrilateral,  or  trapezoidal, 
in  form.  The  bucco-lingual  diameter  is  about  two-ninths 
greater  than  the  mesio-distal.  The  flattened  proximate 
surfaces  converge  toward  the  lingual,  so  that  the  mesio-distal 
measurement  of  the  buccal  portion  is  a  little  greater  than 
the  lino-ual.  The  buccal  and  lingual  mars-ins  are  convex. 
The  buccal  convexity  forms  an  arc  of  about  a  quarter  circle, 
and  merges  into  the  proximate  surfaces  by  obtuse,  but  well- 
defined,  angles  (A,  g).  The  lingual  margin  forms  an  arc  of 
nearly  half  a  circle,  and  merges  into  the  proximate  margins 
without  any  angular  prominence. 


Fig.  30. 


fU^_, 


y^' 


Fig.  33. 


^yue^ 


Wg^  ^u-e/^ 


Fig.  34. 


Fig.  3.5. 


Fig.  30*  (Par.  42).— Left  Upper  First  Bicuspid,  Occlusal  Surface,  a,  Point  of 
iDuecal  cusp ;  b,  lingual  cusp  ;  c,  buccal  ridge ;  d,  mesial  marginal  ridge ;  e,  distal  mar- 
ginal ridge ;  /,  triangular  ridge  of  the  buccal  cusp ;  g,  disto-bucco-occlusal  angle ;  h, 
mesio-bucco-occlusal  angle  ;  i,  triangular  ridge  of  the  lingual  cusp ;  I,  central  groove  ;  o, 
mesial  groove ;  p,  distal  groove ;  n,  m,  triangular  grooves  ;  r,  s,  buccal  grooves. 

Fig.  31*  (Par.  46.).— Left  Upper  First  Bicuspid,  Buccal  Surface,  a,  Buccal  cusp ; 
c,  buccal  ridge ;  e,  e,  buccal  grooves ;  /,  gingival  line ;  g,  mesio-bucco-occlusal  angle ; 
/*,  disto-bucco  occlusal  angle  ;  i,  buccal  root ;  k,  lingTial  root. 

Fig.  32*  (Par.  48).— Right  Upper  First  Bici'spid,  Mesial  Surface,  a,  Buccal  cusp ; 
b,  lingual  cusp ;  c,  mesio-bucco-occlusal  angle  ;  d,  mesial  surface  and  point  where  there  ■ 
is  often  a  concavity ;  /,/,  gingival  line ;  e,  lingual  root ;  g,  buccal  root. 

Fig.  33*  (Pan  50).— UpperFirst  Bicuspid,  vs^ith  three  roots.    Mesio-buccal  angle. 

Fig.  34*  (Par.  50).— Upper  First  Bicuspid,  with  three  short  roots  and  of  a  peculiar 
form. 

Fig.  35*  (Par.  50).— Upper  First  Bicuspid,  with  a  single,  very  long,  crooked  root. 


*  Illustration,  1)^  diameters. 


UPPER    FIRST    15ICUSPID,  45 

43.  The  occlusal  surface  has  two  prominent  cusps — the 
buccal  (a),  and  the  lingual  (6) — and  is  transversed  from  mesial 
to  distal  by  a  deep  sulcus.  The  buccal  cusp  is  the  larger, 
and  forms  the  terminal  point  of  the  buccal  surface.  From 
the  point  of  this  cusp,  four  ridges  lead  away  at  right  angles. 
Two  of  these  form  cutting  edges,  which  slope  away  mesially 
and  distally  to  the  mesio-bucco-occlusal  (A)  and  disto-bucco- 
occlusal  angles  {g),  where  they  join  the  mesial  and  distal 
marginal  ridges.  The  central  buccal  ridge  (c)  leads  away 
centrally  on  the  buccal  surface  toward  the  gingival  line, 
forming  the  convexity  of  this  surface.  The  triangular  ridge 
(/)  slopes  down  to  the  central  part  of  the  crown  and  joins  a 
similar  ridge  from  the  lingual  cusp  (z)  to  form  the  transverse 
ridge,  or  ends  in  a  central  sulcate  groove  (/).  The  lingual 
cusp  (6)  is  in  the  form  of  a  crescent ;  its  convexity  forms  the 
occlusal  margin  of  the  lingual  surface.  Instead  of  a  well- 
detined  point  it  usually  presents  a  blunt  edge,  which  runs 
around  its  elevated  central  portion,  and  joins  with  the  mar- 
ginal ridges  at  both  angles.  The  lingual  triangular  ridge  (i) 
leads  down  from  the  central  point  of  the  cusp  to  the  central 
groove,  to  join  its  fellow  from  the  buccal  cusp  in  the  forma- 
tion of  the  transverse  ridge,  or  is  divided  from  it  by  a  deep 
central  sulcate  groove.  This  ridge  is  seldom  prominent. 
Very  frequently  the  central  incline  of  the  lingual  cusp  is  a 
plain  surface. 

44.  The  mesial  {d)  and  the  distal  (e)  marginal  ridges 
are  strong  ridges  of  enamel  w^hich  rise  in  the  mesial  and 
distal  terminations  of  the  cutting  edges  of  the  buccal  cusp,  and 
form  the  mesial  and  distal  margins  of  the  occlusal  surface. 
»They  join  with  the  ridge  forming  the  lingual  cusp ;  or  they 
are  usually  divided  from  the  latter  by  the  mesial  and  distal 
grooves  ;  though  these  grooves  are  often  indistinct,  especially 
in  teeth  that  have  been  somewhat  worn. 

45.  The  occlusal  surface  of  the  bicuspids  has  five  de- 
velopmental grooves  ;  the  central  (/),  mesial  (o),  distal  (;>), 


46  UPPER    FIRST    BICUSPID. 

mesial  triangular  (m),  and  distal  triangular  (n).  The  central 
groove  is  deeply  sulcate,  and  divides  the  triangular  ridges, 
or  passes  over  their  junction  as  a  shallow  line,  and  sinks  into 
a  triangular  pit  at  either  end.  The  mesial  and  distal  grooves 
are  really  continuations  of  the  central,  which  pass  over  the 
marginal  ridges  as  very  fine  lines,  or  as  more  definite  grooves, 
and  mark  the  boundary  of  the  lingual  lobe.  They  are  rarely 
fissured,  while  the  central  groove  is  frequently  fissured 
throughout  its  course.  The  triangular  grooves,  mesial  (m) 
and  distal  (?z),  run  from  the  mesial  and  distal  pits  toward 
the  mesio-buccal  and  disto-buccal  angles,  dividing  the  mar- 
ginal ridges  from  the  triangular.  They  are  occasionally 
sulcate  in  the  first  part  of  their  course,  and  are  generally 
lost  toward  the  mesio-  and  disto-buccal  angles  by  becoming 
shallower ;  but  in  young,  unworn  teeth  they  can  often  be 
followed  as  a  fine  line  runniuij;  over  the  cuttino;  edo-es  of 
the  buccal  cusp  near  the  angles,  and  leading  into  the  buccal 
grooves  (r,  s).  These  are  the  marks  of  confluence  of  the 
mesial  and  distal  lobes  with  the  middle  lobe.  In  the  central 
incline  of  the  lingual  cusp,  supplemental  grooves  are  often 
seen  meeting  the  triangular  grooves  of  the  buccal  side.  The 
triangular  grooves  are  occasionally  fissured  for  a  short  distance 
from  their  junction  with  the  central. 

46.  The  buccal  surface  of  the  upper  first  bicuspid  (Fig. 
31)  is  similar  to  the  labial  surface  of  the  cuspid  {q.  v.  33). 
The  cusp  is  usually  nearer  the  center  of  the  crown,  and 
generally  somewhat  to  the  distal ;  therefore,  the  cutting 
edges  which  run  from  the  summit  of  the  cusp  to  either 
angle  may  be  of  about  equal  length.  In  some  examples  the 
distal  edge  is  the  longer;  but  usually  the  mesial  edge  is  the 
longer.  In  the  gingival  half  of  its  length  this  surface  is 
smoothly  convex  from  mesial  to  distal ;  but  further  toward 
the  occlusal  margin,  the  buccal  ridge,  which  terminates  in 
the  cusp,  becomes  more  prominent,  and  a  shallow  buccal 
groove  (e,  e)  appears  at  both  sides  of  the  ridge,  or  between 


4**- 


J- 


Fiff.  40. 


Fiar.  41. 


Fig.  36*  (Par.  51).— Right  Upper  Second  Bicuspid,  Occlus.\l  Surface,  o,  Point  of 
buccal  cusp;  &,  lingual  cusp  ;  c,  buccal  ridge  ;  e,  mesial  marginal  ridge ;  rf,  distal  marginal 
ridge  ;  /,  triangular  ridge  of  the  buccal  cusp ;  g,  mesio-bucco-occlusal  angle  ;  h,  disto- 
bucco-occlusal  angle ;  i,  triangular  ridge  of  the  hngual  cusp;  I,  central -groove  ;  m,  n, 
triangular  grooves ;  o,  p,  buccal  grooves. 

Fig.  37*  (Par.  52).— Right  Upper  Second  Bicuspid,  Buccal  Surf.\ce.  a,  Point  of 
buccal  cusp ;  c,  buccal  ridge ;  e,  e,  buccal  grooves ;  /,  gingival  line ;  g,  mesio-bucco- 
occlusal  angle  ;  /;,  disto-bucco-occlusal  angle  ;  i,  body  of  root ;  k,  apex  of  root. 

Fjg.  38*  (Par.  52).— Right  Upper  Second  Bicuspid,  Mesial  Surface,  a,  Buccal  cusp ; 
b,  lingual  cusp  ;  /,  gingival  line ;  i,  groove  in  the  mesial  side  of  the  root. 

Fig.  39*  (Par.  52).— Eight  Upper  Second  Bicuspid,  Distal  Surface,  a,  Buccal  cusp  ; 
b,  lingual  cusp  ;  c,  carious  cavity  near  the  proximate  contact  point ;  /,  gingival  line  ;  i, 
groove  in  distal  side  of  root. 

Fig.  40*  (Par.  53).— Upper  Second  Bicuspid,  with  a  very  crooked  root. 

Fig.  41*  (Par.  53).— Upper  Second  Bicuspid,  with  a  very  short  crook  of  the  root. 


*  Illustration,  IJ^  diameters. 


UPPER   FIRST    BICUSPID.  49 


it  and  the  angles.  This  surface  is  also  considerably  narrowed 
toward  the  gingival  margin,  almost  equally  on  the  mesial 
and  distal,  so  that  the  crown  seems  much  broader  near  the 
occlusal  margin. 

47.  The  lingual  surface  is  regularly  convex  from  mesial 
to  distal.  From  the  gingival  margin  to  the  summit  of  the 
lingual  cusp  it  is  often  a  straight  line ;  but  more  generally  it 
is  slightly  convex,  in  many  examples  almost  as  convex  as  the 
buccal  surface. 

48.  The  mesial  surface  (Fig.  32)  is  much  flattened  from 
buccal  to  lingual,  but  is  generally  slightly  convex  over  its 
whole  extent;  yet  in  many  examples  there  is  a  slight  con- 
cavity near  the  gingival  line.  In  the  direction  from  the 
gingival  line  to  the  occlusal  margin,  this  surface  is  slightly 
convex  through  its  whole  length,  but  not  equally  so  through 
its  buccal  and  lingual  half  The  lingual  portion  is  progres- 
sively more  rounded  toward  the  occlusal  surface ;  while  the 
buccal  portion  is  nearly  straight  to  the  bucco-occlusal  angle.* 

49.  The  form  of  the  distal  surface  agrees  substantially 
with  the  mesial,  but  is  rather  more  convex  in  all  directions 
and  any  concavity  is  rare. 

50.  The  root  of  the  upper  first  bicuspid  is  usually  either 
much  flattened  and  grooved  on  its  mesial  and  distal  sides,  or 
separated  into  two  divisions,  one-third  to  two-thirds  of  its 
length,  making  one  buccal  and  one  lingual  root.  More  than 
half  have  their  roots  thus  divided.  When  separated,  the 
roots  taper  regularly  to  slender  apexes.  When  not  divided, 
the  apex  is  apt  to  be  obtuse.  Occasionally  this  tooth  presents 
three  divisions  of  the  root,  two  buccal  and  one  lingual  (Figs. 
33,  34).  In  some  instances  the  root  of  this  tooth  is  very 
crooked  or  otherwise  distorted  (Fig.  35). 

*  The  form  of  the  proximate  surfaces  is  especially  imporiant  in  making 
contour  fillings,  for  any  concavity  increases  the  difficulty  of  forming  good,  clean 
margins  at  the  gingival  border.  The  unequal  convexity  of  the  buccal  and 
lingual  halves  is  important,  and  requires  a  special  adaptation  of  iuttruments  to- 
make  a  perfect  contour  and  good  clean  margins. 
B 


50  '  UPPER   SECOND   BICUSPID. 

UPPER  SECOND  BICUSPID. 

51.  The  upper  second  bicuspid  so  nearly  resembles  the 
upper  first,  just  described,  that  a  notice  of  its  differences 
will  be  sufficient.  It  is  a  little  smaller,  and  in  every  way 
more  slender.'^  The  general  form  of  the  occlusal  surface 
(Fig.  36)  is  similar  to  the  first  bicuspid.  It  presents  a  buccal 
and  a  lingual  cusp,  and  similar  sulcus,  ridges,  grooves,  and 
pits.  The  average  height  of  the  cusps  is  considerably  less 
than  in  the  first  bicuspid.  The  marginal  ridges  are  propor- 
tionally broader,  the  mesial  and  distal  pits  closer  to  each 
other,  and  the  central  groove  shorter.  The  triangular  grooves 
join  the  central  groove  nearer  the  mesio-distal  center  of  the 
tooth,  making  the  buccal  triangular  ridge  narrow-er  and 
more  nearly  pointed.  In  many  examples  the  enamel  of  the 
occlusal  surface  is  thrown  into  several  shallow  wrinkles,  or 
supplemental  grooves  and  ridges,  which  radiate  from  the 
central  groove,  which  occurs  bat  rarel}^  in  the  first  bicuspid. 
The  buccal  cusp  is  a  little  nearer  the  mesio-buccal  than  the 
disto-buccal  angle,  so  that  the  distal  edge  is  slightly  the 
longer. 

52.  From  mesial  to  distal,  the  buccal  surface  (Fig.  37) 
is  not  so  broad  at  the  occlusal  surface,  and  is  a  little  broader 
at  the  neck,  so  that  it  has  not  so  much  of  the  bell-crown  ap- 
pearance as  the  first  bicuspid.  Otherwise,  this  surface  has 
the  same,  but  less  definitely  defined  outlines  and  markings. 
The  mesial  and  distal  surfaces  (Figs.  38  and  39)  are  generally 
slio-htly  more  convex,  and  the  crown  more  smoothly  rounded. 
The  mesial  surface  seldom  shows  a  concavity.  The  lingual 
surface  is  usually  a  little  more  rounded  toward  the  cutting 
edge  or  crest  of  the  cusp.  Generally,  the  distal  side  of  the 
lingual  cusp  is  rounded  to  such  an  extent  as  to  bring  the 
summit  of  the  cusp  to  the  mesial  of  the  central  line  of  the 
tooth.  The  gingival  line,  in  its  course  round  the  neck  of 
the  tooth,  makes  but  a  slight  labio-lingual  curvature  on  the 

*  The  popular  opinion  is  that  the  second  bicuspid  is  the  larger. 


u^i^* 


Fig-.  46. 


Fig.  47. 


Fig.  42*  (Par.  54).— Right  Lower  First  Bicuspid,  Occlusal  Sueface.  a,  Point  of 
buccal  cusp ;  6,  lingual  cusp  or  ridge  ;  c,  buccal  ridge  ;  d,  mesial  marginal  ridge  ;  c ,  dis- 
tal marginal  lidge ;  ,/,  triangular  ridge  of  buccal  cusp  or  buccal  triangular  ridge ;  f/, 
mesio-bucco-occlusal  angle  ;  /(,  disto-bucco-occlusal  angle  ;  /,  central  groove  crossing  tbe 
transverse  ridge  ;  I,  mesial  pit ;  o,  p,  buccal  grooves. 

Fig.  43*  (Par.  54).— Lower  First  Bicuspid,  Occlus4L  Surface,  a,  Point  of  buccal 
■cusp ;  b,  lingual  cusp  or  ridge ;  a,  triangular  ridge  of  buccal  cusp  deflected  to  one  side ; 
d,  triau.gular  groove  with  fissure ;  f,  mesial  marginal  ridge  ;  /,  distal  marginal  ridge. 

Fig.  44*  (Par.  57).— Right  Lower  First  Bicuspid,  Buccal  Surface,  o,  Buccal  cusp; 
d,  buccal  ridge  ;  e,  €,■  buccal  grooves  ;  ,/",  gingival  line  ;  g,  disto-bucco-occlusal  angle  ;  /(, 
mesio-bucco-occlusal'angie ;  i,  body  of  root ;  k,  apex  of  root. 

Fig.  45*  (Par.  58.)— Left  Lower  First  Bicuspid,  Mesial  Surface,  o,  Buccal  cusp ; 
h,  lingual  cusp  or  ridge ;  o,  distal  marginal  ridge ;  d,  triangular  ridge  of  buccal  cusp  ;  c, 
mesial  marginal  ridge  ;  /,  gingival  line. 

Fig.  46*  (Par.  59).— Left  Lower  First  Bicuspid,  Lingual  Surface,  a,  Buccal  cusp ; 
5  lingual  cusp  or  ridge ;  c,  distal  marginal  ridge  ;  d,  triangular  ridge  of  buccal  cusp  ;  e, 
mesial  marginal  ridge ;  /,  gingival  line. 

Fig.  47*  (Par.  59).— Right  Lower  First  Bicuspid,  Lingual  Surface.  «,  Buccal  cusp ; 
h,  lingual  cusp  or  ridge;  d,  triangular  ridge  of  buccal  cusp;  e,  c,  marginal  ridges;  /, 
gingival  line. 


*  Illustration,  1%  diameters. 


LOWER   FIRST   BICUSPID.  '  53 


mesial  surface.     Generally  there  is  no  curvature  on  the  dis- 
tal surface. 

53.  The  root  of  the  upper  second  bicuspid  is  a  little 
longer  than  the  first,  while  the  crown  is  slightly  shorter, 
which  makes  the  proportionate  increase  of  length  appear 
considerable.  The  root  is  rarely  divided  in  any  part  of  its 
length,  but  is  much  flattened  from  the  neck  to  the  apex. 
The  mesial  side  is  often  deeply  grooved  in  the  apical  third 
of  its  length  ;  the  distal  side  is  less  frequently  grooved.  The 
root  tapers  very  gradually,  remaining  broad  in  the  bucco- 
lingual  diameter,  and  ends  in  a  blunt  apex.  A  few  have  a 
root  that  tapers  rapidly,  becomes  more  rounded,  and  ends  in 
a  slender  apex.  Crooked  roots  are  more  frequent  in  this 
than  in  the  other  bicuspids.     (Figs.  40  and  41.) 

LOWER   FIRST    BICUSPID. 

54.     This  tooth  is  the  smallest  of  the  bicuspids.     The 
occlusal  surface  differs  much  from  the  upper  first  bicus- 
pid.    Indeed,  the   lingual   cusp   is   so   nearly  wanting,  it 
would  hardly  be  called  a  bicuspid  except  for  its  association. 
The  buccal  cusp  is  large  and  prominent,  and  so  much  is  the 
buccal  surface  inclined  lingually,  that,  when  seen  in  a  line 
with  the  long  axis  of  the  tooth,  its  point  occupies  a  position 
about  one-third  distant  from  the  buccal  toward  the  lingual 
outline  of  the  crown  (Figs.  42  and  43).     The  buccal  cusp  pre- 
sents the  same  ridges  leading  from  its  summit  as  described 
for  the  upper  first  bicuspid  (Par.  43),  but  the  pair  which 
form  the  cutting  edges  usually  form  a  curve  with  its  con- 
vexity to  the  buccal,  and  merge  into  the  marginal  ridges  by 
more  rounded  angles.     The  buccal  triangular  ridge  is  nar- 
row and  prominent  (/),  and  joins  the  elevated  lingual  ridge, 
or  cusp  (6),  forming  a  complete  transverse  ridge.     In  many 
instances  this  is  deflected  to  the  mesial  or  distal.     In  young 
teeth,  the  central  groove  often  crosses  the  transverse  ridge  as 
a  fine  line,  which  soon  disappears  by  wear.     However,  in 


54  LOWER    FIRST    BICUSPID. 

many  examples  the  transverse  ridge  is  divided  by  a  deeply 
silicate  groove.  There  is  a  deep  pit  at  the  mesial  and  the 
distal  ends  of  the  central  groove,  or  on  either  side  of  the 
transverse  ridge  (c,  d)  from  "which  the  triangular  grooves, 
which  divide  the  marginal  ridges  from  the  triangular,  or 
transverse  ridge,  ran  toward  the  mesio-  and  disto-buccal 
angles.  These  are  often  sulcate  in  the  first  part  of  their 
course.  In  many  young  teeth  these  grooves  may  be  traced 
over  the  cutting  edges  onto  the  buccal  surface,  marking 
the  contiuence  of  the  central  with  the  mesial  and  distal  buccal 
lobes. 

55.  The  lingual  lobe  varies  much  in  its  size  and  out- 
line. It  is  divided  from  the  three  buccal  lobes  by  the 
mesial, distal, and  central  grooves;  and  often  occupies  but  a 
small  portion  of  the  lingual  margin  of  the  occlusal  surface. 
The  grooves  which  mark  its  outlines  are  often  indistinct, 
and  often  obliterated  by  wear.  The  lobe  may  form  a  ridge 
of  even  height,  and  join  the  marginal  ridges,  or  it  may  be 
elevated  into  one  or  more  tubercles.  It  may,  also,  be  raised 
into  a  small  cusp,  located  centrally,  or  to  either  side  of  the 
central  line  of  the  tooth. 

56.  The  marginal  ridges  are  occasionally  quite  small, 
but  in  most  examples  they  are  well  developed,  and  cause  the 
mesial  and  distal  surfaces  to  stand  out  prominently,  giving 
the  tooth  a  strong,  bell-crowned  appearance.  The  length  of 
the  marginal  ridges  varies  Avith  the  size  of  the  lingual  lobe. 

57.  The  buccal  surface  (Fig.  44)  is  convex  in  all  direc- 
tions. The  cu'^p  is  to  the  distal  of  the  perpendicular  line 
and  its  figure  similar  to  the  upper  first  bicuspid,  except  that 
its  surface  is  more  convex.  As  the  occlusion  is  directlj^  on 
the  point  of  the  cusp,  as  with  the  anterior  lower  teeth  gen- 
erally, it  is  soon  so  worn  down  that  its  prominence  is  lost. 

58.  The  mesial  and  distal  surfaces  are  convex  from 
buccal  to  lingual.  In  the  direction  from  the  occlusal  mar- 
gin to  the  gingival  line,  they  are  generally  concave,   after 


LOWER    SECOND    BICUSPID.  55 

passing  the  convexity  of  the  immediate  occlusal  margin. 
This  latter  stands  out  boldly  to  both  mesial  and  distal,  giv- 
ing a  marked  bell-crowned  form.  The  concavity  of  the 
mesial  and  distal  surfaces  is  not  so  well  seen  from  the  buccal 
view  as  from  the  lino;;ual.  The  greater  over-hang  of  the 
crown  (over  the  root),  and  the  greater  concavity,  are  toward 
the  lingual  portion. 

59.  The  lingual  surface  (Figs.  46  and  47)  is  smoothly 
rounded  from  mesial  to  distal,  and  slightly  convex  in  the 
direction  of  the  length  of  the  tooth.  It  is  only  about  half 
as  long  as  the  buccal  surface  (in  unworn  teeth),  and  when 
viewed  at  right  angles  with  the  long  axis  of  the  tooth,  all  of 
the  occlusal  surface  on  the  lingual  side  of  the  buccal  cusp 
is  seen  except  the  pits  and  sulci. 

60.  The  neck  of  the  tooth  is  much  constricted,  and  has 
a  deep  gingival  line.  This  makes  the  proper  adjustment  of 
a  band  for  an  artificial  crown  particularly  difficult.  The  cur- 
vature of  the  gingival  line  is  much  less  than  in  the  upper 
first  bicuspid,  the  average  being  less  than  one  millimeter  {q^ 
V.  table  of  measurements). 

61.  The  root  of  this  tooth  is  somewhat  flattened  at  the 
neck,  on  lines  that  converge  rapidly  toward  the  lingual,  and 
often  grooved  on  its  mesial  and  distal  sides,  and  sometimes 
the  root  is  bifurcated.  It  tapers  regularly,  with  a  tendency 
to  a  more  nearly  round  form  at  the  apex,  and  generally  ends 
in  a  slender  point. ,  The  root  is  generally  straight,  or  the 
lingual  surface  is  straight,  and  the  buccal  surface  convex. 
This  convexity  extends  from  the  apex  of  the  root  to  the 
point  of  the  crown,  which  gives  that  characteristic  appear- 
ance so  peculiar  to  the  anterior  lower  teeth. 

LOWER   SECOND    BICUSPID. 

62.  The  lower  second  bicuspid  is  a  little  longer  than 
the  lower  first,  and  of  much  the  same  figure,  except  that  the 
lingual  cusp  is  proportionately  higher  and  more  nearly,  but 


66  LOWER    SECOND    BICUSPID. 

never  quite,  on  a  level  with  the  buecal,  but  the  lingual  sur- 
face is  about  equal  to  the  buccal  in  mesio-distal  breadth. 
These  teeth  are  regular  in  general  contour,  but  the  grooves 
of  the  occlusal  surface  are  much  diversified.  These  diiFer- 
enees  may  be  classified  under  three  forms  :  1st.  The  central 
groove  joins  the  triangular  grooves  in  such  a  way  as  to  form 
a  half  circle  with  the  convexity  to  the  lingual,  with  or  with- 
out a  transverse  ridge  crossing  its  line.  In  these,  when  the 
transverse  ridge  is  high,  only  a  deep  pit  appears  on  either 
side  (Fig.  48).  2d.  The  lingual  cusp  is  divided  by  a  sulcate 
groove,  which  runs  over  centrally,  or  nearly  so,  to  the  lingual 
surface,  making  a  three-cusped  tooth  (Fig.  49).  The  central 
groove  forms  an  angle  at  the  junction  with  the  lingual,  or  is 
crescentic  in  form.  It  joins  with  the  triangular  grooves  in 
such  a  way  that  the  point  of  junction  cannot  be  told  except 
by  finding  the  mesial  and  distal  grooves,  which  are  often 
very  indistinct.  3d.  The  central  groove  is  straight,  and 
generally  sulcate,  with  a  deep  pit  at  each  end.  In  many 
examples  these  pits  are  crossed  by  the  triangular  grooves 
almost  at  right  angles  with  the  central  (Fig.  50).  By  tracing 
the  fine  mesial  and  distal  grooves  carefully  in  young  unworn 
teeth,  it  will  be  found  that  the  lingual  lobe  is  much  larger 
than  in  the  lower  first  bicuspid,  and  almost  as  large  as  in 
the  upper  bicuspids.  In  the  three-cusped  forms  the  two 
lingual  lobes  are  usually  a  little  broader  from  mesial  to  dis- 
tal than  the  buccal  portion  of  the  tooth. 

63.  The  buccal  surface  (Fig.  51)  of  the  lower  second 
bicuspid  does  not  differ  from  the  other  bicuspids,  except  in 
being  shorter,  the  cusp  lower.  The  lingual  surface  (Fig.  52) 
is  broader  and  smoothly  convex ;  in  the  three-cusped  forms 
it  is  often  somewhat  flattened  and  grooved  in  its  occlusal 
third,  giving  the  crown  a  squarish  appearance,  or  even  trian- 
gular when  the  lingual  lobes  are  large. 

64.  The  mesial  and  distal  surfaces  in  these  bicuspids 
are  a  little  flattened,  but  remain  convex  from  buccal  to  lingual. 


Fiff.  48. 


Fis.  49. 


Fiff.  50. 


.   9*1/4^^^ 


Mg.  5l 


Fiar.  53. 


Fig.  48*  (Par.  62).— Left  Lower  Second  Bicuspid,  Occlusal  Sueface.  a,  Buccal 
cusp  ;  b,  lingual  cusp  or  ridge  ;  c,  e,  marginal  ridges ;  d,  /,  pits  ;  g,  h,  triangular  grooves. 

Fig.  49*  (Par.  62).— Right  Lowee  Second  Bicuspid,  Occlusal  Sueface,  with  three 
cusps,  a,  Buccal  cusp ;  5,  mesio-lingual  cusp ;  c,  disto-lingual  cusp  ;  d,-  lingual  groove ; 
e,  e,  mesial  and  distal  grooves. 

Fig.  50*  (Par.  62).— Right  Lower  Second  Bicuspid,  Occlusal  Surface,  with  straight 
•central  groove,  a,  Buccal  cusp ;  6,  lingual  cusp ;  c,  e,  marginal  ridges ;  cl,  triangular 
ridge  of  the  buccal  cusp  ;  /,  central  groove  ;  (j,  h,  triangular  grooves. 

Fig.  51*  (Par.  63).— Left  Loavee  Second  Bicuspid,  Buccal  Sueface.  a,  Buccal  cusp ; 
d,  buccal  ridge  ;  e,  c,  buccal  grooves ;  /,  gingival  line ;  g,  mesio-bucco-oeclusal  angle ;  h, 
•disto-bucco-oeclusal  angle  ;  i,  body  of  root ;  k,  apex  of  root. 

Fig.  52*  (Par.  63).— Left  Lowee  Second  Bicuspid,  Lingual  Surface,  a,  Buccal  cusp ; 
&,  ling-ual  cusp  ;  c,  distal  marginal  ridge ;  d,  triangular  ridge  of  the  buccal  cusp ;  e,  mesial 
marginal  ridge  ;  /,  gijigival  line. 

Fig.  53*  (Par.  64).— Left  Lowee  Second  Bicuspid,  Mesial  Sueface.  a,  Buccal  cusp ; 
b,  lingual  cusp ;  d,  triangular  ridge  ;  e,  mesial  marginal  ridge  ;  /,  gingival  line  ;  i,  groove 
in  mesial  side  of  the  root. 


*  Illustration,  1J4  diameters. 


THE  MOLAR  TEETH — THE  UPPER  MOLARS.        59 


From  the  occlusal  margin  to  the  gingival  line,  they  are  nearly 
straight,  though  some  are  convex  and  some  in  part  concave. 
65.  The  root  of  the  lower  second  bicuspid  is  larger  and 
longer  than  that  of  the  first  bicuspid.  It  is  flattened  on  the 
mesial  and  distal  surfaces  on  nearly  parallel  lines,  and  in  some 
examples  concave  or  grooved.  In  rare  instances  the  root  of 
this  tooth  is  deeply  grooved  on  the  buccal  and  lingual  sides, 
with  a  tendency  to  a  division  into  a  mesial  and  distal  prong. 
In  the  greater  number  it  tapers  regularly  to  a  slender  apex, 
but  in  many  the  apex  is  large  and  obtuse.  The  root  is  gen- 
erally straight,  but  occasionally  very  crooked. 

THE   MOLAR    TEETH. 

Q6.  The  molar  teeth  are  very  different  in  form  and  plan 
of  construction  from  those  previously  described.  They  are 
particularly  designed  for  grinding  or  comminuting  food  ;  for 
this  purpose  they  have  broad  occlusal  surfaces,  broken  by 
ridges,  grooves,  and  fossse.  The  ridges  are  raised  at  inter- 
vals into  powerful  cusps,  Avhich  fit  with  more  or  less  accuracy 
into  the  sulci  and  fossae  of  the  opposing  teeth.  There  are 
twelve  molars,  three  on  each  side  of  the  upper  jaw  and  three 
on  each  side  of  the  lower  jaw.  They  are  the  sixth,  seventh 
and  eighth  teeth  from  the  median  line,  and  are  commonly 
named  the  first,  second  and  third  molars,  upper  and  lower. 
The  last  is  also  called  the  wisdom  tooth,  or  Dens  Sapieniia. 
The  upper  and  lower  molars  are  much  alike  in  size  and  gen- 
eral contour,  but  in  the  detail  of  the  arrangement  of  their 
lobes,  cusps,  fossae  and  grooves,  they  are  different.  It  will, 
therefore,  be  necessary  to  describe  the  upper  and  lower  molars" 
separately. 

THE    UPPER    MOLARS. 

67.  The  three  upper  molars  are  similar,  but  present 
minor  differences  of  detail,  consisting  mostly  in  a  less  pro- 
nounced, or  typical  development  of  certain  parts,  or  lobes,  of 
the  second  and  third  molars  (Fig.  62).    The  upper  first  molar 


60 


UPPER    FIRST    MOLAR. 


being  the  typical  form,  will  be  described  first,  and  afterward 
the  deviations  from  this  type  that  occur  in  the  second  and 
third  molars. 

JJPPER    FIRST    MOLAR. 

68.  The  occlusal  surface  of  the  upper  first  molar  (Fig. 
54),  when  seen  in  a  line  with  the  long  axis  of  the  tooth,  pre- 
sents an  outline  of  irregular  rhombic  form,  with  the  mesio- 
buccal  and  disto-lingual  as  acute  angles.  The  angles  are 
rounded,  with  more  or  less  convexity  of  the  marginal  lines. 
This  surface  presents  two  principal  fossae,  and  four  develop- 
mental grooves.  These  grooves  divide  the  crown  into  four 
lobes,  or  primary  developmental  parts,  each  of  which  is  sur- 
mounted by  a  strong  cusp.  These  lobes,  or  cusps,  are  the 
mesio-buccal  (Fig.  54,  a),  disto-buccal  (/^),  mesio-lingual  (c), 
and  disto-lingual  {d).  Of  the  grooves  which  outline  these 
parts,  three  rise  from  the  central  pit  of  the  central  fossa : 
The  mesial  (A),  which  runs  to  the  mesial  margin  ;  the  buccal 
(i),  which  runs  in  a  deep  sulcus  to  the  buccal  margin,  and 
over  it  onto  the  buccal  surface;  and  the  distal  (J),  which 
runs  distally,  and  lingually,  (5ver  the  oblique  ridge  and  ends 
in  the  distal  fossa  (//).  The  remaining  groove — the  disto- 
lingual  (/.-,  k) — begins  a  little  to  the  buccal  of  the  central  part 
of  the  distal  margin,  and  runs  diagonallj^  in  a  straight  line, 
or  in  a  curve  with  the  concavity  toward  the  disto-lingual 
angle,  to  the  lingual  margin,  and  over  it  onto  the  lingual 
surface,  to  become  the  lingual  groove.  Except  that  part  cross- 
ing the  distal  marginal  ridge,  this  groove  is  usually  deeply 
sulcate. 

69.  In  their  origin,  each  lobe  begins  its  calcification  as 
a  separate  piece,  plate,  or  cusp,  and  moves  apart  from  the 
others  as  growth  proceeds,  till  the  proper  dimensions  of 
the  occlusal  surface  are  attained ;  then  the  plates  coalesce 
on  the  lines  marked  by  the  grooves  named  above,  and  thus 
complete  the  occlusal  surface.  When  the  union  has  been 
completed,  nothing  but  fine  lines  remain,  which,  on  any  plain 


Fiff.  57. 


Fis-.  58. 


Fig.  54*  (Par.  68). —Right  Upper  First  Molar,  Occlu.s.\l  Surface,  with  four  cusps. 
o,  Mesio-buccal  cusp  ;  h,  disto-buccal  cusp ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual  cusp  ; 
/,  mesial  marginal  ridge  ;  g,  distal  marginal  ridge  ;  h,  mesial  groove ;  i,  buccal  groove  ;  j, 
distal  groove;  k,  k,  disto-lingual  groove;  m,  mesio-buccal  triangular  groove;  n,  disto- 
buccal  triangular  ridge  ;  this  unites  with  the  distal  ridge  from  the  lingual  cusp  to  form 
the  oblique  ridge;  o,  disto-buccal  triangular  groove,  p,  mesio-buccal  triangular  ridge; 
q,  central  pit.  , 

Fig.  55*  (Par.  70).— Right  Tpper  First  Molar,  Occlusal  Surface,  with  five  cusi;«. 
a,  Mesio-buccal  cusp  ;  &,  disto  buccal  cusp  ;  c,  mesio-lingual  cusp ;  d,  disto-lingTial  cusp  ; 
e,  tilth  cusp ;  /,  mesial  marginal  ridge  ;  g,  distal  marginal  ridge  ;  /;,  mesial  groove ;  ), 
buccal  groove ;  j,  distal  groove ;  k,  k,  disto-lingual  groove ;  I,  k,  mesio-lingual  groove  ; 
the  lingual  cusps  are  faceted  by  wear ;  m,  mesio-buccal  triangular  groove ;  n,  disto- 
buccal  triangular  ridge. 

Fig.  56*  (Par.  78).— Right  Upper  First  Molar,  Buccal  Surface,  a,  Mesio-buccal 
cusp ;  b,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual  cusp  ;  c,  buccal  ridge  ; 
/,  gingival  line  ;  g,  mesio-bucco-occlusal  angle  ;  /;,  disto-bucco-occlusal  angle  ;  i,  buccal 
groove  ;  k,  mesial  root ;  I,  distal  root ;  m,  lingual  root. 

Fig.  57*  (Par.  79). — Right  Upper  First  Molar,  Lingual  Surface,  o,  Mesio-buccal 
cusp ;  h,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp  ;  d,  disto-liogual  cusp ;  e,  fifth  cusp ; 
/,  gingival  line ;  g,  disto-lingual  groove ;  h,  mesio-lingual  groove ;  i,  lingual  groove ; 
k,  mesial  root ;  /,  distal  root ;  m,  lingual  root. 

Fig.  58*  (Par.  80).— Right  Upper  First  Molar,  Mesial  Surface,  a,  Mesio-buccal 
cusp  ;  b,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp  :  c,  fifth  cusp  ; 
/,  /,  gingival  line  ;  //,  mesio-lingual  groove  ;  k,  mesial  root ;  I,  distal  root ;  m,  lingual 
root. 

*  Illustration,  IJ^  diameters. 


UPPER   FIRST   MOLAR.  63 


parts,  are  often  quickly  obliterated  by  wear.  But  on  parts 
meeting  at  an  angle,  forming  a  sulcus,  as  in  the  buccal  and 
disto-lingual  grooves,  there  is  usually  a  sharp  groove,  and  at 
any  point  where  the  union  has  been  imperfect,  there  is  a 
fissure.*  Fissures  are  most  frequent  at  the  ends  of  the 
grooves,  near  the  central  pit,  or  where  they  are  deeply  sul- 
cate,  and  in  the  central  portion  of  the  disto-lingual  groove ; 
but  they  may  occur  in  any  part  of  these  lines. 

70.  In  many  examples  of  the  upper  first  molars,  but  in 
no  others,  there  is  a  small  fifth  lobe  or  cusp  (Fig.  55,  e). 
This  is  situated  on  the  lingual  side  of  the  mesio-lingual  lobe, 
from  which  it  is  divided  by  a  fifth  groove,  the  mesio-lingual 
(/,  /t),  which  runs  from  the  lingual  portion  of  the  mesial 
margin  diagonally  to  the  lingual  margin,  and  joins  the  lin- 
gual groove.  This  cusp,  when  it  occurs,  is  always  bilateral, 
i.  e.,  on  both  the  right  and  left  upper  first  molars.  It  is 
hereditary,  appearing  regular!}"  in  the  teeth  of  children  when 
present  in  the  teeth  of  both  parents.  It  occurs  also,  in  a 
modified  form,  when  present  in  but  one  parent.  Therefore, 
the  cusp  will  be  found  in  all  possible  varieties  of  develop- 
ment, from  its  largest  size,  as  represented  in  Fig.  55,  to  the 
merest  line  marking  its  position  on  the-  lingual  side  of  the 
mesio-lingual  cusp. 

71.  The  occlusal  surface  of  the  upper  first  molar  has  four 
marginal  ridges,  broken  by  the  grooves  described  (Par.  68), 
so  as  to  form  four  principal  eminences  or  cusps.  These  are 
the  buccal,  lingual,  mesial,  and  distal  marginal  ridges.  Of 
these,  the  mesial  and  distal  marginal  ridges  are  close  upon 
the  margins  of  the  surface.  But  the  buccal  and  lingual  are 
carried  toward  the  central  line  of  the  tooth  by  the  inclination 
of  the  buccal  and  lingual  surfaces.     In  the  upper  molars  the 

*  In  large  strong  teeth  it  seems  that  the  growth  of  the  dentine  pulp  is  often 
too  great  for  the  enamel  cap,  so  that  the  enamel-forming  cells  are  drawn  apart 
preventing  a  union  of  the  enamel  plates;  hence  fissures  are  more  frequent  in 
large  teeth. 


64  UPPER   FIRST   MOLAR. 


central  inclination  of  the  linsjual  surface  is  mucli  sjreater 
than  that  of  the  buccal ;  while  in  the  lower  molars  the  cen- 
tral inclination  of  the  buccal  surface  is  the  greater.  The 
buccal  marginal  ridge  begins  at  the  mesio-buccal  angle,  in 
the  form  of  a  blunt  cutting  edge,  and  rises  in  a  curved  line 
to  the  summit  of  the  mesio-buccal  cusp  (Fig.  o4,  a),  from 
which  it  descends  distally  to  the  buccal  groove  {i).  From  the 
summit  of  this  cusp  the  mesio-buccal  triangular  ridge  (p) 
descends  to  the  mesial  side  of  the  central  pit  (q).  This  ridge 
is  divided  from  the  mesio  marginal  ridge  by  the  mesio-buccal 
supplemental  groove  (?7i),  which  is  sometimes  deep,  but  gen- 
erally shallow,  and  occasionally  absent.  From  the  buccal 
groove  the  marginal  ridge  rises  rapidly  to  the  summit  of  the 
disto-buccal  cusp  (6),  then  descends  in  a  curve  to  the  disto- 
buccal  angle,  to  join  the  distal  marginal  ridge  {<j).  From  the 
point  of  this  cusp  the  disto-buccal  triangular  ridge  (or  trian- 
gular ridge  of  the  disto-buccal  cusp,  ?z),  runs  down  to  the 
distal  side  of  the  central  pit,  where  it  joins  a  ridge  from  the 
mesio-lingual  cusp  to  form  the  oblique  ridge,  or  is  divided 
from  this  ridge  by  a  sulcate  distal  groove. 

72.  The  lingual  marginal  ridge  begins  at  the  mesio- 
lingual  angle  as  a  rounded  edge,  and  rises  in  a  curve  to  the 
summit  of  the  mesio-lingual  cusp  (c),  and  descends,  continu- 
ing its  curve,  into  a  ridge,  meeting  the  triangular  ridge  of 
the  disto-buccal  cusp  to  form  the  oblique  ridge.  However, 
in  a  less  pronounced  form,  this  marginal  ridge  descends  from 
the  summit  of  the  mesio-lingual  cusp  to  the  distal,  where  it 
is  deeply  broken  by  the  disto-lingual  groove.  On  the  distal 
side  of  this  groove  it  rises  "abruptly  to  the  summit  of  the 
disto-lingual  cusp  (c/),  from  which  it  slopes  away  in  a  curve 
to  join  the  distal  marginal  ridge. 

73.  The  mesial  marginal  ridge  (/)  is  a  strong  band  of 
enamel  running  from  the  mesio-buccal  to  'the  mesio-lingual 
angle  of  the  occlusal  surface.  It  forms  the  mesial  boundary 
of  the  occlusal  surface,  and  the  angle  of  junction  of  the  mesial 


UPPER    FIRST   MOLAK.  65 

and  occlusal  surfaces,  or  the  mesio-occlusal  angle.  It  is  low 
in  the  center  of  its  length,  and  rises  toward  both  angles.  It 
is  crossed  near  its  center  b}^  the  mesial  groove,  usually  as  a 
fine  line,  which  is  often  obliterated  by  wear  early  in  life. 
Occasionally  one  or  more  small  tubercles  appear  in  the  central 
portion  of  this  ridge,  inclosed  in  what  seems  to  be  a  division 
of  the  mesial  groove. 

74.  The  distal  marginal  ridge  {g)  is  a  band  of  enamel 
forming  the  distal  boundary  of  the  occlusal  surface,  from 
angle  to  angle,  and  forms  the  angle  of  junction  between  the 
occlusal  and  the  distal  surfaces,  or  the  disto-occlusal  angle. 
It  is  low  in  the  center  of  its  course,  and  is  crossed  by  the 
distal  end  of  the  disto-lingual  groove  as  a  fine  line,  usually  a 
little  to  the  buccal  of  the  central  point. 

75.  The  central  fossa  is  irregularly  circular,  and  is 
formed  by  the  central  inclines  of  the  mesial  marginal  rido-e, 
mesio-buccal  cusp,  disto-buccal  cusp,  mesio-lingual  cusp,  and 
oblique  ridge.  It  is  made  irregular,  and  sometimes  angular, 
by  the  depth  of  the  several  sulcate  grooves,  or  by  the  jorora- 
inence  of  the  triangular  ridges,  especially  that  from  the 
mesio-buccal  cusp.  The  central  incline  of  the  mesio-lino-ual 
cusp  is  generally  a  plane  surface,  but  is  sometimes  slightly 
concave,  and  in  about  a  fourth  of  its  examples  there  is  a  low, 
triangular  ridge  running  from  its  apex  directly  to  the  central 
pit.  The  oblique  ridge  is  occasionally  cut  through  by  a  deep 
and  wide  distal  sulcus,  thus  connecting  the  central  with  the 
distal  fossa.  In  a  few  examples  two  supplemental  grooves  or 
wrinkles  arise  from  the  mesial  groove  at  about  the  center  of 
its  length,  and  run,  one  toward  the  mesio-buccal,  and  the 
other  toward  the  mesio-lingual  angle  of  the  occlusal  surface. 
These  are  often  of  such  depth  and  width  as  to  form  a  small 
supplemental  mesial  fossa.  Of  these  grooves,  the  mesio-lingual 
is  generally  absent,  and  the  mesio-buccal  (m)  is  generally 
present,  though  often  very  shallow. 

76.  The  distal  fossa  is  formed  by  the  distal  incline  of 


66  UPPER   FIRST   MOLAR. 


the  disto-buccal  and  mesio-lingual  cusps  and  oblique  ridge, 
which  meet  the  central  incline  of  the  disto-lingual  cusp  and 
distal  marginal  ridge.  It  is  traversed  by  the  disto-lingual 
groove,  which  is  generally  sulcate,  and  deepens  into  a  pit  at 
the  point  where  it  receives  the  distal  groove.  From  the 
buccal  portion  a  supplemental  groove,  the  disto-buccal,  runs 
well  up  toward  the  summit  of  the  disto-buccal  cusp,  dividing 
its  triangular  ridge  from  the  distal  marginal  ridge. 

77.  In  some  molars  many  supplementgl  grooves  or 
wrinkles  radiate  from  the  centers  of  these  fossfe  on  the  in- 
clines of  the  ridges  and  cusps,  and  in  some  poorly  developed 
teeth  these  are  deeply  fissured.  The  growth  of  enamel  seems 
to  have  reached  out  toward  the  line  of  junction  in  the  form 
of  spiculce,  and  to  have  failed  to  fill  out  the  space. 

78.  The  buccal  surface  of  the  upper  first  molar  (Fig. 
56)  is  irregularly  convex.  Its  length  is  about  equal  to  the 
mesio-distal  breadth  at  the  gingival  line,  while  the  width  at 
the  widest  point,  near  the  occlusal  margin,  is  about  three- 
tenths  greater.  Therefore,  the  mesial  and  distal  margins 
converge  toward  the  neck.  The  mesial  margin  is  almost 
straio-ht,  after  the  rounding  of  its  mesio-occlusal  angle,  but 
the  distal  is  convex.  The  occlusal  margin  is  surmounted  by 
the  buccal  cusps  {a,  6),  between  which  there  is  a  deej^  notch, 
through  which  the  buccal  groove  passes  from  the  occlusal  to 
the  buccal  surface.  This  groove  passes  centrally  toward  the 
gingival  line  about  half  the  length  of  this  surface,  dividing 
the  occlusal  portion  into  a  mesial  and  distal  buccal  ridge. 
In  some  examples  the  groove  continues  across  the  gingival 
line  to  the  bifurcation  of  the  roots.  There  is  a  bucco-gingi- 
val  ridge  of  enamel  {e)  near  the  gingival  line  which  the 
buccal  groove  generally  does  not  cross.  The  mesio-distal 
convexity  is  greatest  on  this  ridge,  and  diminishes  toward 
the  occlusal  margin.  The  summit  of  this  convexity  is  on 
the  mesial  half,  in  a  line  with  the  mesial  root,  and  the  surface 
falls  away  rapidly  toward  the  disto-buccal  angle  of  the  tooth. 


Fig.  59. 


Fig.  60. 


Fig.  61. 


Fig.  59*  (Par.  81). -Right  Upper  First  Molar,  Distal  Surface,  a,  Mesio-buccal 
<!usp;  6,  disto-buccal  cusp;,  d,  disto-lingual  cusp  ;  /, /,  gingival  line;  k,  mesial  root; 
t,  mstal  root ;  m,  lingual  root ;  o,  concavity  of  the  distal  surface. 

Fig.  60*  (Par.  82). -Left  Upper  First  Molar,  Buccal  Surface.  A  bell-crowned 
tooth. 

Fig.  61*  (Par.  85j.-Upper  First  Molar  showing  the  mesial  and  distal  roots  united 
at  their  apexes. 

FiG._62*(Par.  86).-The  RroiiT  Upper  Molars  showing  the  progressive  diminution 
ot  the  disto-liiigual  cusp  from  the  first  to  the  third  molar. 


*  Illustration,  ly^  diameters. 


UPPER    FIRST    MOLAR.  69 


79.  The  lingual  surface  (Fig.  57)  is  divided  in  a  line 
with  the  long  axis  of  the  tooth  into  a  mesial  and  distal  lobe 
by  the  lingual  groove  {i).  Both  lobes  are  smoothly  convex 
from  mesial  to  distal,  and  in  a  less  degree  from  the  gingival 
line  (/)  to  the  occlusal  margin.  The  gingival  line  is  nearly 
horizontal,  and  so  sunken  as  to  give  the  appearance  of  a  gin- 
gival enamel  rido;e.  The  occlusal  maro-in  is  surmounted 
by  the  mesio-  and  disto-lingual  cusps  (c,  d),  of  which  the 
mesial  is  usually  the  larger.  In  the  five-cusped  molar  ihe 
fifth  cusp  (e)  is  seen  on  the  mesio-lingual  lobe.  The  mesial 
and  distal  margins  are  convex,  converging  rapidly  toward 
the  lingual  root.  In  the  few  examples  in  which  the  lingual 
groove  is  not  apparent,  the  lingual  surface  is  smoothly  con- 
vex from  mesial  to  distal. 

80.  The  mesial  surface  (Fig.  58)  is  nearly  flat  in  all 
directions,  and  its  margins  are  rounded  to  the  buccal  and  lin- 
gual surfaces.  Toward  the  occluso-buccal  angle,  the  flat  sur- 
face is  continued  well  up  to  the  occlusal  surface,  which  it 
meets  in  a  fairly  sharp  angle  ;  but  as  it  approaches  the  linguo- 
occlusal  portion  it  is  progressively  rounded  toward  the  oc- 
clusal surface.  In  many  molars,  near  the  gingival  line,  half 
way  from  buccal  to  lingual,  this  surface  is  a  little  concave.   , 

81.  The  distal  surface  (Fig.  59),  in  its  lingual  half,  is 
convex  in  all  directions,  but  in  its  buccal  half  there  is  often 
a  concavity  formed  by  a  considerable  distal  protrusion  of  the 
disto-lingual  lobe.  This  is  a  shallow,  but  marked,  depression 
(o),  running  from  the  bifurcation  of  the  distal  and  the  lingual 
roots  toward  the  disto-buccal  cusp.  It  crosses  the  gingival 
line  at  a  point  about  one-third  distant  from  the  buccal  to- 
w^ard  the  lingual  margin.  In  many  examples  this  dej)ression 
is  more  central,  and  receives  the  distal  termination  of  the 
disto-lingual  groove,  which  may  often  be  traced  as  a  fine  line 
nearly  or  quite  to  the  gingival  border  of  the  enamel.  This 
complication  of  the  surface  makes  the  finishing  of  fillings, 
and  the  fitting  of  bands  loi-  crowns,  specially  difficult.     This 


70  UPPER    FIRST   MOLAR. 


depression  falls  short  of  forming  a  concavity  in  about  one- 
fourth  of  the  first  molars. 

82.  The  root  of  the  upper  first  molar  (Figs.  56  to  61) 
is  divided  into  three  prongs  or  roots* — the  mesial,  or  mesio- 
buccal  (k),  the  distal  or  disto-buccal  (l),  and  the  lingual  (m). 
These  are  usually  quite  widely  separated,  giving  the  tooth  a 
firm  seat  in  its  alveolus.  The  lingual  root  is  the  largest ;  it 
diverges  boldly  to  the  lingual,  and  is  straight,  or  slightly 
curved,  with  the  convexity  to  the  lingual.  It  is  conical,  and 
taj^ers  regularly  to  an  obtuse  rounded  apex.  In  most  molars 
it  has  a  groove,  a  continuation  of  the  lingual,  on  its  lingual 
side,  running  nearly,  or  quite,  its  whole  length.  In  rare 
examples  this  root  bifurcates. 

83.  The  mesial  root  (/.)  is  larger  than  the  distal ;  broad 
from  buccal  to  lingual,  and  thin  from  mesial  to  distal,  with 
the  lingual  portion  the  thinner,  and  grooved  on  its  fiattened 
sides.  It  diverges  first  to  the  mesial  and  buccal,  and  tben 
curves  to  the  distal.  It  tapers  mostly  at  the  expense  of  the 
lingual  thin  edge,  and  ends  in  a  fiattened  or  rounded  apex. 

84.  The  distal  root  (/)  is  the  smallest  of  the  three.  It 
diverges  to  the  distal  and  buccal,  and  is  straight,  or  slightly 
curved,  sometimes  to  the  distal,  sometimes  to  the  mesial,  so 
that  its  apex  approaches  the  mesial  root.  It  is  fiattened  on 
its  mesial  and  distal  sides,  but  less  than  the  mesial  root,  and 
tapers  to  a  more  rounded  form,  ending  in  a  slender  point. 

85.  The  roots  of  the  first  molar  are,  perhaps,  more 
regular  in  form  than  those  of  any  other  of  the  molar  teeth  ; 
but  even  in  these,  considerable  deviation  from  the  forms  de- 
scribed will  occasionally  be  observed  (Figs.  60  and  61). 

*  The  divibions  of  the  root  of  a  tooth  are  usually  called  "the  roots,"  and 
the  upper  molars  are  said  to  have  three  roots.  The  neck  of  the  tooth  is,  how- 
ever, common  to  all,  and,  more  strictly,  there  is  one  root  divided  into  several 
prongs,  or  fangs.  Some  authors  follow  this  form  of  expression.  For  instance, 
Prof.  Judd  says:  "The  root  of  a  molar  is  divided  into  three  fangs."  T  see  no 
good  reason,  however,  for  not  calling  them  roots,  the  term  generally  in  use  by 
the  dental  profession. 


Fig.  63. 


Fig.  65. 


Fig.  66. 


Fig.  67. 


Fig.  63*  (Par.  86).— Eight  Upper  Seccxd  Molar,  Occlusal  Si-rface,  with  three  of 
the  cusps  faceted  by  wear.  Tooth  large  and  especially  well  developed,  o,  Mesio-buccal 
cusp ;  b,  disto  buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp  ;  /,  mesial  mar- 
ginal ridge  ;  g,  distal  margiual  ridge  ;  h,  mt  sial  groove  ;  /,  buccal  groove ;  j,  distal  groove  ; 
k,  disto-lingual  groove  ;  /,  distal  fossa ;  m,  mesio-buccal  triangular  groove ;  n,  central  pit ; 
o,  mesio-buccal  triangular  ridge  ;  p,  disto-buccal  triangular  ridge  ;  )-,  mesio-lingual  tri- 
angular ridge.  * 

Fig.  64*  (Par.  86).— Right  Upper  Second  Mol.4.r,  Occlusal  Surface.  Tooth  of 
medium  size  and  imperfect  form,  a,  Mesio-buccal  cusp ;  b,  disto-buccal  cusp ;  c,  mesio- 
lingual  cusp  ;  d,  disto-lingual  cusp ; ./',  mesial  marginal  ridge  ;  (i,  distal  marginal  ridge ; 
/*,  mesial  groove ;  i,  baccal  groove  ;  I,  distal  fossa.  The  disto-lingual  groove  is  imperfect ; 
m,  mesio-buccal  triangular  groove;  o,  mesio-buccal  triangular  ridge ;  p,  disto-buccal  tri- 
angular ridge,  which  unites  with  the  ridge  from  the  mesio-lingual  cusp  to  form  the 
oblique  ridge. 

Fig.  65*  (Par.  87)— Right  Upper  Second  Molar  showing  a  form  of  deformity  pecu- 
liar to  this  tooth  that  is  not  very  common. 

Fig.  66*  (Par.  89).— Right  Upper  Second  Molar  with  the  roots  inclined  to  the 
distal. 

Fig.  67*  (Par.  90).— Right  Upper  Second  Molar,  Distal  Surface,  with  the  three 
roots  compressed  into  one. 

Fig.  68*  (Par.  90).— Right  Upper  Second  Molar,  showing  the  distal  and  lingual 
roots  united. 


■  Illustration,  Iji  diameters. 


UPPER   SECOND   MOLAR.  73 

UPPER  SECOND  MOLAR. 

86.  The  most  constant  difference  between  the  occlusal 
surfaces  of  the  upper  first  and  second  molars  is  that  the 
latter  tooth  is  smaller,  and  has  an  almost  constant  tendency 
to  a  relatively  smaller  size  of  the  disto-  lingual  lobe.  This 
tendency  is  well  seen  in  Fig.  62,  in  which  the  upper  molars 
of  a  very  well  formed  denture  are  drawn  from  the  cast. 
This  shows  the  disto-lingual  lobe  progressively  diminished, 
so  that  in  the  third  molar  it  is  very  small.  When  a  large 
number  of  second  molars  are  examined,  it  is  found  that  the 
central  fossae  are  not  so  regularly  formed  as  in  the  first,  being 
often  small,  even  in  large,  well-developed  teeth  (Fig.  63), 
and  the  cusps  comparatively  low,  with  a  relatively  greater 
inclination  of  the  lingual  surface  toward  the  summit  of  the 
mesio-lingual  cusp.  In  manj'-  examples  the  distal  fossa  is 
reduced  to  a  mere  pit  (Fig.  64),  and  the  lingual  marginal 
ridge  is  continued  from  the  summit  of  the  mesio-lingual 
cusp  distally  to  the  disto-lingual  angle,  where  it  joins  the 
distal  marginal  ridge,  as  in  Fig.  64,  making  practically  a 
three-cusped  tooth.  In  many  of  these,  after  the  tooth  is  a 
little  worn,  the  clisto-lingual  groove  cannot  be  traced  across 
the  lingual  marginal  ridge,  nor  on  the  lingual  surface  ;  but  a 
fine  line  is  generally  seen  crossing  the  distal  marginal  ridge. 

87.  The  upper  second  molar  is  liable  to  a  peculiar 
deformity,  which  I  have  not  seen  in  any  other  tooth.  The 
■crown  is  greatly  flattened  from  mesial  to  distal,  occasionally 
to  such  an  extent  as  to  present  none  of  its  usual  lines.  In 
the  extreme  cases  (Fig.  65)  there  is  one  central,  long-shaped 
sulcus  running  from  buccal  to  lingual, formed  by  the  central 
inclines  of  a  ridsfe  encirclino;  the  occlusal  surface.  This 
ridge  may  be  broken  at  intervals  by  shallow  grooves  crossing 
it.  Usually,  much  of  the  central  inclination  of  this  ridge 
is  wrinkled,  and  often  there  are  many  small  fissures.  The 
mesial  surface  is  commonly  deeply  concave,  and  the  distal 
■convex. 


74  UPPER   THIRD  MOLAR. 


88.  In  well-developed  second  molars,  the  form  of  the 
buccal,  lingual,  mesial,  and  distal  surfaces  is  much  the 
same  as  in  the  first  molar,  though  rather  more  convex, 
and  concavities  in  the  mesial  and  distal  surfaces  are  not  so 
frequent.  However,  in  teeth  with  large  disto-lingual  cupps, 
the  concavity  of  the  distal  surface  is  about  the  same  as  in 
the  first  molar  (Par.  81).  The  lingual  groove  is  generally  not 
sulcate,  though  it  is  usually  seen  .as  a  fine  line  in  unworn 
teeth.  It  is  often  near  the  disto-lingual  angle,  and,  when 
sulcate,  it  generally  disappears  by  becoming  shallower  about 
half-waj''  toward  the  gingival  line  ;  rarel}^  it  runs  across  the 
gingival  line,  and  in  that  case  the  lingual  root  is  grooved, 
as  in  the  first  molars. 

89.  The  neck  of  the  tooth  is  less  regular  in  its  outline 
than  in  the  first  molar.  In  the  average,  it  is  more  flattened 
from  mesial  to  distal,  and  on  lines  that  converge  more  to  the 
lingual.  On  the  buccal  surface,  the  mesio-buccal  ridge  is 
relatively  more  prominent,  and  at  the  neck  the  surface  slopes 
away  more  toward  the  distal,  so  that  in  many  examples,  the 
distal  root  seems  compressed  between  the  mesial  and  lingual 
roots. 

90.  The  roots  of  this  tooth  are  the  same  in  number  and 
general  form  as  in  the  first  molar ;  but  they  spread  less,  and 
are  curved  more  to  the  distal  (Fig.  Q6).  There  is  also  much 
more  variety  of  the  comparative  size  of  the  root  and  crown 
than  in  the  first  molar.  In  many  the  root  is  single,  with  the 
outlines  of  the  division  marked  by  grooves  of  variable  depth 
(Fig.  67);  or  two  of  the  roots  may  be  connected,  while 'the 
third  is  free.  Sometimes  this  union  is  the  lingual  with  the 
distal  (Fig.  68) ;  but  oltener  it  is  the  lingual  with  the  mesial 
root. 

UPPER   THIRD   MOLAR. 

91.  The  upper  third  molar  deviates  from  the  typical 
form  of  the  first  more  than  does  the  second.  Yet,  in  dent- 
ures of  the  best  form,  it  presents  the  same  developmental 


O,    ,G  ,C 


Fig.  69. 


Fig.  72. 


Fig.  73. 


Fig.  69*  (Par.  91)  —Right  Upper  Third  Molar,  Occlusal  SrEFACE,  of  typical  form. 
a,  Mesio-buccal  cusp  ;  b,  disto-buccal  cusp  ;  c,  mesio-liiigual  cusp  ;  d,  disto-liugnal  cusp  ; 
e  mesial  marginal  ridge  ;  .A  distal  marginal  ridge  ;  r/,  mesio-buccal  triangular  ridge  ;  h, 
disto-buccal  triangular  ridge ;  i,  mesial  groove ;  k.  buccal  groove  ;  I,  distal  groove ;  m. 
disto-lingual  groove ;  n,  central  pit ;  o,  mesio-buccal  triangular  groove. 

Fig.  70*  (Par.  91).— Right  L'pper  Third  Molar,  Occlusal  Surface,  three  cusped. 
a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  lingual  cusp ;  e,  mesial  marginal  ridge ; 
h,  distal  marginal  ridge  ;  i,  mesial  groove  ;  k,  buccal  groove  ;  I,  distal  groove ;  o,  mesio- 
buccal  triangular  groove. 

Fig.  71*  (Par.  91).— Right  Upper  Third  Molar,  Occlusal  Surface.  Young,  unworn 
tooth  of  Imperfect  form,  o,  :Mesio- buccal  cusp ;  h,  disto-buccal  cusp ;  c,  lingual  cusp;  e, 
mesial  marginal  ridge ;  /,  distal  marginal  ridge  ;  g,  mesial  groove  ;  h,  buccal  groove  ;  i, 
distal,  groove.    Several  supplemental  .grooves  are  seen  radiating  from  the  central  pit. 

Fig.  72*  (Par.  94).— Right  Upper  Third  Molar,  Buccal  Surface.  The  roots  are  not 
quite  complete,  and  show  the  funnel-shaped  openings  at  the  apex. 

Fig.  73*  (Par.  94).— Left  Upper  Third  Molak  with  five  roots. 


*  Illustration,  13^  diameter? 


UPPER   THIRD   MOLAR.  77 

lines,  fosspe,  and  cusps  (Fig.  69).  The  disto-lingual  lobe  is 
very  much  smaller,  and  in  many  examples  is  entirely  want- 
ing. Of  the  examples  in  my  possession,  about  twenty-one 
per  cent,  show  a  diminutive  disto-lingual  cusp ;  thirty-two 
per  cent,  show  a  pit  in  the  position  of  the  distal  fossa,  and 
some  portion  of  the  disto-lingual  groove,  but  no  depressed 
groove  over  the  lingual  marginal  ridge ;  it  is  similar  to  that 
shown  in  Fig.  64.  The  remainder,  or  about  forty-seven  per 
cent.,  have  no  disto-lingual  lobe.  *0f  the  latter,  three-fourths 
are  properly  three-cusped  teeth  in  which  the  oblique  ridge 
becomes  the  distal  marginal  ridge,  and  the  distal  groove  runs 
over  to  the  distal  surface  (Fig.  70).  In  the -remainder,  there 
is  only  an  irregular  ridge  (Fig.  71),  forming  a  central  fossa, 
so  marked  with  wrinkles  or  supplemental  grooves  that  the 
developmental  lines  are  not  satisfactorily  made  out.  Many 
examples  of  the  three-cusped  teeth  show  much  relative  dimi- 
nution of  the  disto-buccal  lobe. 

92.  The  upper  third  molar  is  the  smallest  of  the  mo- 
lars,* and  is  more  irregular  in  its  size  and  conformation  than 
the  first  or  the  second  molar.  On  account  of  the  small  size 
of  the  disto-lingual  lobe,  the  distal  portion  of  the  tooth  is 
much  smaller  than  the  mesial,  and  in  the  three-cusped  teeth 
the  crown  becomes  triangular,  with  its  angles  well  rounded. 
(Fig.  70.) 

93.  The  mesial  surface  resembles  that  in  the  upper  first 
and  second  molars,  but  is  more  rounded,  so  that  a  concave 
portion  is  less  frequent,  and  the  distal  surface  is  well  rounded. 
The  lingual  and  buccal  surfaces  are  more  rounded  than  the 
same  surfaces  in  the  other  upper  molars.  The  gingival  line 
is  usually  horizontal  in  its  course  around  the  neck  of  the 
tooth,  except  that,  in  a  few  examples,  there  is  a  slight  curva- 
ture on  the  mesial  slirface.  Many  upper  third  molars  are 
much  flattened  from  mesial  to  distal.  These  generally  have 
a  considerable  concavity  on  the  mesial  surface.    Occasionally 

*  Forty  upper  first  molars  balanced  sixty  upper  third  molars. 


78  THE    LOWER   MOLARS — THE    LOWER   FIRST   MOLAR. 


teetla  are  found  that  are  also  abnormally  small  and  have  the 
appearance  of  supernumeraries.  More  rarely  this  tooth  fails 
to  develop,  and  is  wanting  entirely. 

94.  The  root  of  the  upper  third  molar  has,  in  the  more 
regular  forms,  the  three  divisions  common  to  the  upper  mo- 
lars, though  relatively  smaller  and  not  so  widely  separated  as 
those  of  the  first  and  second  molars ;  and  often  end  in  slender 
conical  points  ;  many  have  but  a  single  root;  but  in  most  of 
these  the  three  roots  are  oiAlined  by  grooves  of  more  or  less 
depth.  A  considerable  number  have  more  than  three  roots, 
which  are  irregular  in  size  or  form  (Fig.  73).  Four,  five, 
six,  and  even  seven  or  eight  divisions  are  sometimes  met. 
The  neck  is  then  generally  broad  from  buccal  to  lingual,  and 
the  occlusal  surfa^ce  of  the  crown  irregularly  formed.  Many 
of  the  three  cusped  teeth  have  the  root  without  divisions. 

THE    LOWER   MOLARS. 

95.  The  lower  molars  differ  so  much  from  each  other, 
especially  the  first  and  second,  that  each  must  be  separately 
described. 

THE  LOWER  FIRST  MOLAR. 

96.  The  lower  first  molar  is  the  sixth  tooth  from  the 
median  line  in  the  lower  jaw.  It  proximates  the  lower  second 
bicuspid  with  its  mesial  surface,  and  the  lower  second  molar 
with  its  distal.  'Next  to  the  upper  first  molar,  it  is  the  larg- 
est tooth  in  the  denture.*  The  outline  of  the  occlusal  sur- 
face (Figs.  74  and  75),  when  seen  in  a  line  with  the  long  axis 
of  the  tooth,  is  trapezoidal,  with  the  buccal  marginal  line 
the  longest.  The  buccal  angles  are  about  equally  acute,  while 
the  lingual  angles  are  equally  obtuse,  and  all  are  more  or  less 
rounded.  The  buccal  margin  is  convex,  but  made  irregular 
by  two  buccal  grooves.  The  lingual  margin  is  nearly  straight, 
but  sometimes  slightly  concave,  or  notched  in  the  center  of 
its  length,  by  the  lingual  groove ;  but  more  generally  it  is 

*  Forty-two  upper  first  molars  balanced  forty-six  lower  first  molars. 


Fig.  74. 


^       /  tX 


Fig  7b 


Fig.  77. 


Fig.  74*  (Par.  96'.— Left  Lower  First  Molar,  Occlusal  Stieface,  of  typical  form. 
a,  jNIesio-buccal  cusp  ;  h,  disto-buceal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ; 
e,  distal  cusp  ;  /,  mesial  marginal  ridge ;  g,  distal  marginal  ridge ;  /(,  mesio-buccal  tri- 
angular ridge ;  /,  disto-buccal  triangular  ridge ;  k,  disto-ling-ual  triangular  ridge ;  I, 
me>io-lingual  triangular  ridge;  m,  distal  triangular  ridge  ;  n,  mesial  groove  ;  o,  buccal 
groove ;  p,  disto-buccal  groove  ;  ;■,  distal  groove  ;  s,  lingual  groove. 

Fig.  75*  (Par.  96).— Right  Lower  First  Molar,  Occlusal  Surf.^ce.  a,  Mesio-buccal 
cusp ;  b,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual  cusp :  e,  distal  cusp ; 
/,  mesial  marginal  ridge  ;  g,  distal  marginal  ridge  ;  li,  mesial  triangular  ridge  ;  i,  disto- 
buccal  triangular  ridge ;  k,  mesio-lingual  triangular  ridge ;  I,  disto-lingual  triangular 
ridge;  ti,  mesial  groove;  o,  buccal  groove;  p,  disto-buccal  groove;  r,  distal  groove;  ?, 
lingual  groove  ;  t,  mesio-buccal  triangular  groove. 

Fig.  76*  (Par.  104).— Left  Lower  First  Molar,  Buccal  Surface,  a,  Mesio-buccal 
cusp ;  6,  disto-buccal  cusp ;  c,  distal  cusp ;  rf,  bucco-gingival  ridge ;  e,  buccal  pit ;  /, 
gingival  line  ;  g,  mesial  root ;  h,  distal  root ;  ;,  buccal  groove  ;  k,  disto-buccal  groove. 

Fig.  77*  (Par.  104).— Left  Lower  First  Molar,  Buccal  Surface,  with  prominent 
cusps.    References  the  same  as  for  Fig.  76. 


•  Illustration,  1)^  diameters. 


THE    LOWER    FIRST    MOLAR.  81 


slightly  convex.  The  mesial  and  the  distal  margins  are  nearly 
straight  in  the  best  formed  teeth  ;  though  the  distal  is  some- 
times considerably  convex,  as  the  fifth,  or  disto-lingual  cusp 
is  more  or  less  prominent.  All  of  these  margins  vary  as  to 
their  convexity ;  the  rule  being  that,  in  teeth  of  large  size 
and  symmetrical  development,  they  approach  nearer  to 
straight  lines. 

97.  Each  of  these  marginal  portions  is  "surmounted  by 
the  mesial,  buccal,  lingual,  and  distal  marginal  ridges,  which 
form  a  continuous  elevation  of  irregular  height  around  the 
margins  of  the  occlusal  surface,  and  on  which  there  are  five 
cusps.  The  central  inclinations  of  these  ridges  form  the 
central  fossa.  On  the  mesial,  lingual,  and  distal,  the  sum- 
mits of  these  ridges  are  close  on  the  margins  of  the  surface ; 
but  on  the  buccal,  there  is  an  inclination  of  the  buccal  surface 
that  carries  the  summit  of  the  ridge  considerably  toward  the 
central  axis  of  the  tooth. 

98.  The  occlusal  surface  has  five  developmental 
grooves  (Figs.  74  and  75)— the  mesial,  buccal,  disto-buccal, 
lingual,  and  distal—which  divide  it  into  five  developmental 
parts,  or  lobes.  These  are  the  mesio-buccal  (a),  disto-buccal 
(6),  mesio-lingual  (c),  disto-lingual  {d),  and  distal  (e)  lobes ; 
each  bearing  a  cusp  of  the  same  name.  The  mesial  groove 
(n)  runs  from  the  central  fossa  over  the  mesial  marginal 
ridge  to  the  mesial  surface.  On  the  mesial  marginal  ridge 
it  is  usually  a  fine  line  which  is  soon  obliterated  by  wear. 
Occasionally,  this  is  divided  into  two  branches,  with  a  small 
tubercle  on  the  mesial  marginal  ridge  between  them  (Fio-. 
74,/).  In  many  examples  there  is  a  supplemental  groove 
which  rises  from  the  mesial  groove  at  about  the  center  of  its 
length,  and  runs  toward  the  mesio-buccal  angle.  This  is  the 
mesio-buccal  triangular  groove  (Fig.  75,  t).  It  divides  the 
mesial  marginal  ridge  from  the  triangular  ridge  of  the 
mesio-buccal  cusp.  ]\J[ore  rarely  there  is  also  a  similar 
groove    running    toward    the    mesio-lingual   cusp.      When 


82  THE    LOWER    FIRST   MOLAR. 

these  are  deep,  they  form  a  mesial  supplemental  fossa  (Fig. 
75,  t).  The  buccal  groove  (o)  runs  in  a  deep  sulcus  from 
the  central  pit  to,  and  over,  the  buccal  marginal  ridge  to 
the  buccal  surface,  and  divides  the  mesio-buccal  from  the 
disto-buccal  cusp.  The  disto-buccal  groove  (p)  also  runs 
bucco-distally  from  the  central  pit  over  the  buccal  ridge,  more 
or  less  near  the  distal  angle,  as  the  distal  cusp  is  large  or 
small.  It  divides  the  disto-buccal  lobe  from  the  distal.  The 
lingual  groove  is)  runs  from  the  central  pit  in  a  deep  sulcus 
to,  and  over,  the  lingual  marginal  ridge  onto  the  lingual  sur- 
face, and  divides  the  two  lingual  lobes.  The  distal  groove 
(r)  runs  distally  over  the  distal  marginal  ridge,  and  divides 
the  disto-lingual  lobe  from  the  distal.  Frequently  this  groove 
can  be  traced  some  distance  toward  the  gingival  line  on  the 
distal  surface.  The  mesial  and  distal  grooves  form  a  line 
traversing  the  whole  extent  of  the  occlusal  surface,  from 
mesial  to  distal,  in  the  center  of  which  a  V-sliaped  deflection 
is  formed  with  its  point  to  the  lingual,  the  base  receiving  the 
point  of  the  triangular  ridge  (?')  of  the  disto-buccal  cusp. 

99.  In  most  examples,  the  central  fossa  occupies  all 
the  occlusal  surface  within  the  circle  of  the  sumndt  of  the 
marginal  ridges,  though,  occasionally,  one  or  more  supple- 
mental fossffi  are  divided  from  it  by  high  triangular  ridges 
running  down  from  the  cusps  (Fig.  75,  h,  k).  The  surface 
of  the  fossa  is  made  irregular  in  most  of  these  teeth  by  deep 
sulci  on  the  lines  of  the  grooves,  separating  the  cusps  and 
triangular  ridges. 

100.  The  occlusal  surfaceof  the  lower  flrst  molar  has  five 
cusps,  one  on  each  of  the  five  lobes,  or  three  on  the  buccal 
marginal,  and  two  on  the  lingual  marginal  ridge."'  These 
€usps  are  formed  by  the  grooves  previously  described  (Par. 
98),  which  pass  over  the  ridges  in  depressions  of  variable 
depth,  thus  subdividing  the  crests  of  the  ridges  into  obtuse 

*  In  some  rare  cases  lower  first  molars  ha'W  but  four  cusps,  and  then  the 
tooth  is  like  the  lower  second  molar.     (Pars.  109,  110.) 


THE    LOWER   FIRST   MOLAR. 


elevations.  Usually,  these  are  not  so  high  and  prominent  as 
the  Gusps  of  the  upper  molars.  The  mesio-buccal  (Figs.  74 
and  75,  a)  is  the  largest  and  strongest  of  the  buccal  cusps, 
and  occupies  rather  more  than  one-third  of  the  buccal  mar- 
ginal ridge.  From  its  crest  a  triangular  ridge  (A)  runs  down 
centrally  to  the  junction  of  the  mesial  and  buccal  grooves, 
-and  is  divided  from  a  similar  triano-ular  ridg-e  from  the 
mesio-lingual  cusp,  by  the  mesial  groove.  When  these  two 
ridges  are  high,  they  form,  in  conjunction  with  triangular 
grooves  between  them  and  the  mesio-marginal  ridge,  a 
mesial  supplemental  fossa.  The  disto-buccal  cusp  (b)  is  of 
less  extent  from  mesial  to  distal,  but  has  a  long-er  triano-ular 
ridge,  though  not  so  high,  which  ends  in  the  point  of  the 
V-shaped  deflection  of  the  mesial  and  distal  grooves,  or  at 
their  junction. 

101.  The  lingual  cusps  (c,  d)  are  about  equal  in  size 
and  height  (perhaps  the  mesial  is  a  little  the  higher  on  the 
average).  They  have  strong  triangular  ridges  (k,l)  wdiich 
terminate  in  the  angles  formed  by  the  junction  of  the  lin- 
gual groove  with  the  mesial  and  distal  grooves  in  the  central 
pit. 

102.  The  distal  cusp  (e)  occupies  the  distal  portion  of 
the  buccal  ridge,  and  forms  the  disto-buccal  angle  of  the 
occlusal  surface.  It  is  the  distinguishing  mark  of  the 
lower  first  molar,  being  but  very  rarely  absent  in  that  tooth, 
and  never  present  in  the  lower  second  molar.  It  is  the 
smallest  of  the  five  cusps,  and  varies  most  in  its  relative  size. 
In  some  examples  it  is  almost  or  quite  as  large  as  the  disto- 
buccal  cusp.  In  others,  especially  in  small  and  poorly-de- 
veloped teeth,  it  may  be  reduced  to  a  mere  tubercle,  occupy- 
ing the  buccal  portion  of  the  distal  marginal  ridge  and  the 
immediate  disto-buccal  angle.  The  central  incline  of  this 
cusp  is  commonly  nearly  flat,  but  occasionally  has  a  rounded 
crest.  It  ends  in  a  point  at  the  junction  of  the  distal  and 
■disto-buccal  grooves. 


84  THE    LOAVER    FIRST    MOLAR. 

103.  Ill  this  tooth  there  is  often  a  deep  pit  at  the  junc- 
tion of  the  mesial,  distal,  and  lingual  grooves.  Less  fre- 
quently there  is  also  a  pit  at  the  junction  of  the  mesial  and 
buccal  grooves,  and  at  the  junction  of  the  distal  and  disto- 
buccal  grooves.  The  grooves  are  often  fissured  for  a  short 
distance  from  the  pits,  especially  in  the  deeply  sulcate  lingual 
groove.  In  some  very  poorly  developed  teeth  fissures  may 
be  found  in  any  part  of  the  grooves. 

104.  The  buccal  surface  of  the  lower  first  molar  (Figs. 
76  and  77),  when  seen  at  right  angles  with  the  long  axis  of  the 
tooth,  is  irregularly  trapezoidal  in  form,  with  the  occlusal 
margin  about  two-sevenths  longer  than  the  gingival.  The 
mesial  and  distal  margins  converge  toward  the  gingival, 
and  the  angles  with  the  occlusal  surface  are  about  equally 
acute.  The  occlusal  margin  is  broken  into  three  eleva- 
tions, or  cusps,  by  the  buccal  and  disto-buccal  grooves. 
The  gingival  line  is  straight,  or  slightly  curved,  with  the 
concavity  toward  the  occlusal  surface.  The  mesial  and  the 
distal  lines  are  slightly  convex.  The  buccal  surface  is  con- 
vex in  all  directions ;  but  the  line  of  convexity  from  mesial 
to  distal  is  broken  toward  the  occlusal  margin  by  the 
buccal  and  disto-buccal  grooves,  which  pass  over  from  the 
occlusal  surface.  The  buccal  groove  {i)  is  usually  a  little 
to  the  mesial  of  the  central  line  of  the  surface,  and  often  ends 
in  a  deep  pit  (e),  about  half-way  from  the  occlusal  to  the 
gingival  margin.  Exceptionally,  this  groove  is  continued 
to  the  bifurcation  of  the  root.  The  disto-buccal  groove  (k) 
is  near  the  disto-buccal  angle,  and  its  course  is  toward  the 
gingival  line,  with  a  distal  inclination.  It  is  usually  lost  to 
sight  by  becoming  shallower,  but  in  some  examples  it  may 
be  traced  to  the  gingival  line.  The  enamel  terminates  in  a 
marked  inclination  toward  the  gingival  line,  forming  the 
bucco-gingival  ridge. 

105.  The  lingual  surface  of  this  tooth  (Figs.  78  and  79) 
is  slightly  convex  in  all  directions.     It  forms  a  fairly  sharp 


Fig.  78. 


Fig.  79. 


Fig.  81. 


Fig.  78*  (Par.  105).— Left  Lower  First  Molar,  Lingual  Surface,  a,  Mesio-buccal 
cusp  ;  b,  disto-buccal  cusp  ;  c,  distal  cusp ;  d,  mesio-lingual  cusp ;  e,  disto-lingual  cusp  ; 
/,/,  gingival  line;  r/,  mesial  root;  /;,  distal  root;  the  roots  are  spread  wide  apart;  i, 
lingual  groove. 

Fig.  79*  (Par.  105).— Left  Lower  First  Molar,  Lingual  Surface.  This  tooth  has 
prominent  cusps,  and  the  roots  are  straight  and  close  together.  References  the  same  as 
for  Fig.  78. 

Fig.  80*  (Par.  106).— Left  Lower  First  Molar,  Mesial  Surface,  a,  Mesio-buccal 
cusp  ;  d,  mesio-lingual  cusp ;  e,  mesial  surface,  point  of  concavity  ;  /,  /,  gingival  line  ; 
g,  mesial  root  with  broad  groove. 

Fig.  81*  (Par.  107).— Left  Lower  First  Molar,  Distal  Surf.ace.  The  cusps  are 
very  prominent,  a,  Mesio-buccal  cusp ;  &,  disto-buccal  cusp ;  c,  distal  cusp ;  d,  mesio- 
lingual  cusp ;  e,  disto-lingual  cusp ;  /,  gingival  line  ;  g,  mesial  root ;  h,  distal  root. 

Fig.  82*  (Par.  108).— Lower  First  Molar,  with  three  roots. 


*  Illustration,  IJ^  diameters. 


THE    LOWER   FIRST    MOLAR.  87 


angle  with  the  occlusal  surface,  but  is  rounded  away  toward 
the  mesial  and  distal  surfaces.  On  account  of  the  lingua) 
convergence  of  the  mesial  and  distal  surfaces,  the  lingual 
surface  is  much  shorter  mesio-distallj  than  the  buccal.  The 
occlusal  margin  is  deeply  notched  by  the  passage  of  the 
lingual  groove  (i),  which  usually  terminates  near  the  center 
of  the  surface  by  becoming  shallower. 

106.  The  mesial  surface  (Fig.  80)  is  very  irregular  in 
outline,  and  often  the  occlusal  margin  is  deeply  concave. 
The  gingival  curvature  is  generally  marked,  and  the  buccal 
and  lingual  marginal  lines  convex.  The  buccal  margin  of 
this. surface  is  more  convex  than  the  lingual,  and  its  curva- 
ture is  at  such  an  incline  as  to  render  the  gingival  marginal 
line  much  longer  than  the  occlusal.  The  surface  is  slightly 
convex,  though  almost  flat ;  but,  in  the  central  portion,  near 
the  eino-ival  line,  it  is  sometimes  slightly  concave  from  buccal 

"^  •Til 

to  lingual.  It  is  rounded  away  toward  the  mesio-buccal  and 
mesio-lingual  angles.  AVith  the  occlusal  surface  it  forms  a 
sharp,  angle  in  the  central  portion,  but  this  is  rounded  in  its 
buccal  and  lingual  portions.  In  the  direction  of  the  long 
axis  of  the  tooth,  there  is  usually  a  concavity  at  the  junction 
of  the  enamel  and  cementum. 

107.  The  distal  surface  (Fig.  81)  is  smoothly  convex 
from  buccal  to  lingual.  From  the  occlusal  surface  to  the 
gingival  line  it  is  straight  or  slightly  convex,  but  forms  a 
considerable  concavity  at  the  junction  of  the  crown  with  the 
root,  which  occasionally  forms  a  sharp  angle,  but  generally 
is  well  rounded.  The  occlusal  margin  is  often  deeply  notched 
by  the  distal  groove.  In  a  few  examples  the  disto-buccal 
groove  is  deep  after  passing  over  the  marginal  ridge,  and  in 
its  distal  inclination  forms  a  slight  concavity  near  the  disto- 
buccal  angle. 

108.  "  The  root  of  the  lower  first  molar  is  divided  into 
two  prongs  (Figs.  76  to  82),  and  this  division  is  usually  close 
to  the  crown,  closer  than  in  any  other  tooth  in  the  mouth. 


THE    LOWER    SECOND   MOLAR. 


The  mesial  root  {g)  inclines  first  to  the  mesial,  and  then 
curves  regularly  toward  the  distal.  It  is  broad  from  buccal 
to  lingual,  and  is  much  thinned  from  mesial  to  distal,  so  that 
in  cross  sections  it  measures  double  as  much  one  way  as  the 
other.  It  is  usually  slightly  concave  on  both  mesial  and  dis- 
tal surfaces,  and  tapers  regularly,  but  not  rapidly,  from  the 
bifurcation  to  the  apex,  and  ends  in  a  flattened,  but  well 
rounded,  point.  The  distal  root  (A)  inclines  to  the  distal  at 
first,  and  afterward  is  nearly  or  quite  straight.  In  some  ex- 
amples the  apical  half  curves  to  the  distal,  but  more  often 
toward  the  mesial,  so  that  the  ajDCxes  of  the  two  roots  are 
inclined  toward  each  other.  It  is  narrower  from  buccal  to 
lingual  than  the  mesial  root,  and  more  nearly  round,  being 
but  rarel}^  concave  or  grooved  on  either  mesial  or  distal  sur- 
face. It  tapers  quite  regularly,  and  more  nearly  to  a  point 
than  the  mesial  root,  though  the  apex  is  generally  well 
rounded.  The  form  of  the  root  is  regular,  rarely  deviating 
much  from  its  type.  Occasional!}',  however,  the  division  of 
the  root  is  incomplete.  The  mesial  root  is  occasionally  di- 
vided, giving  the  tooth  three  roots  (Fig.  82);  and  I  have 
seen  a  few  in  which  the  distal  root  was  divided  also,  giving 
four  roots. 

THE  LOWER  SECOND  MOLAR. 

109.  The  most  characteristic  ditterence  between  the 
lower  first  and  second  molars  is  the  absence  of  the  fifth 
lobe  in  the  second,  and  the  general  change  of  form  which 
this  absence  implies ;  the  other  parts  of  the  tooth  being 
similar. 

110.  When  the  occlusal  surface  is  seen  in  a  line  with 
the  long  axis  of  the  tooth  (Fig.  83),  the  outline  of  the  crown 
is  nearly  a  parallelogram,  with  angles  rounded  and  the  lines 
slightly  convex,  the  buccal  most.  The  summits  of  the  mar- 
ginal ridges  are  close  to  the  mesial,  distal,  and  lingual  mar- 
gins, while  the  buccal  is  carried  over  toward  the  lingual  by 
the  inclination  of  the  buccal  surface.     The  central  inclines  of 


Fig.  87. 


djL    ''~t 


Fig.  86. 


Fig.  89. 


Fig.  83*  (Par.  110).— Right  Lower  Second  Molar,  Occlusal  Surface,  of  typical 
form,  o,  Mesio-buccal' cusp ;  6,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp :  d,  disto-lingual 
cusp  ;  c,  mesial  marginal  ridge ;/,  distal  marginal  ridge  ;  cu  mesio-buccal  triangular  ridge  ; 
/i,  disto-buccal  triangular  ridge ;  i,  mesio-lingual  triangular  ridge ;  A-,  disto-lingual  trian- 
gular ridge  ;  I,  mesial  groove  ;  in,  buccal  groove ;  n,  lingual  groove ;  o,  distal  groove. 

Fig.  8-t*  (Par.  113).— Right  Lower  Second  Molar,  Occlusal  Surface,  of  imperfect 
form.  «,  Mesio-buccal  cusp  ;  6,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual 
cusp ;  e,  mesial  marginal  ridge ;  /,  distal  marginal  ridge  ;  r/,  mesio-buccal  triangular  ridge  ; 
1\,  disto-buccal  triangular  riSge ;  ?:,  mesio-liagual  triangular  ridge  ;  A.-,  disto-lingual  trian- 
gular ridge  ;  I,  mesial  groove  ;  ?»,  buccal  groove ;  n,  lingual  groove  ;  o,  distal  groove. 

Fig.  85*  (Par.  115>.— Left  Lower  Second  Molar,  Buccal  Surface,  a,  Mesio-buccal 
cusp  ;  &,  disto-buccal  cusp  ;  c,  buccal  groove  ;  d,  buccal  pit ;  /,  gingival  line ;  g,  mesial 
loot ;  h,  distal  root. 

Fig.  86*  (Par.  116).— Left  Lower  Second  Mol.vr,  Lingual  Surface,  a,  Mesio-buccal 
cusp  ;  6,  disto-buccal  cusp ;  c,  mesio-lin  jual  cusp  ;  cZ,  disto-lingual  cusp  ;  e,  lingual  groove  ; 
/,  gingival  line  ;  rj,  mesial  root ;  h,  distal  root. 

Fig.  87*  (Par.  117).— Left  Lower  Second  Molar,  Mesi.\l  Surface,  a,  Mesio-buccal 
cusp  ;  c,  mesio-lingual  cusp ;  d,  point  of  proximate  contact  of  mesial  surface  ;  /,  gingival 
line ;  g,  mesial  root. 

Fig.  88*  (Par.  118).— Left  Lower  Second  Molar,  Distal  Surface.  «,  Mesio-buccal 
cusp  ;  h,  disto-buccal  cusp ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual  cusp  ;  e,  point  of  proxi- 
mate contact  of  the  distal  surface  ;  /,  gingival  line ;  h,  distal  root. 

Fig.  89*  (Par.  119^.— Right  Lower  Second  Mol.vr,  Lingual  Surface.  The  roots  are 
curved  very  much  to  the  distal. 

*  Illustration,  1^  diameters. 


THE   LOWER   SECOND   MOLAR.  91 

the  marginal  ridges  form  a  deep  central  fossa,  in  the  center 
of  which  there  is  usually  a  deep  pit. 

111.  There  are  four  developmental  grooves,  all  arising 
from  the  central  pit.  The  mesial  groove  (l)  runs  to  the  me- 
sial margin  and  crosses  the  mesial  marginal  ridge  as  a  line 
line,  which  is  often  obliterated  by  wear.  The  distal  groove 
(o)  runs  in  a  similar  Avay  to  the  distal  surfece.  These  two 
grooves  divide  the  occlusal  surface  from  mesial  to  distal,  and 
centrally,  between  the  summits  of  the  buccal  and  lingual 
marginal  ridges.  The  buccal  groove  (m)  runs  from  the  cen- 
tral pit  to  the  buccal  margin,  and  over  it  to  the  buccal  sur- 
face, dividing  the  buccal  ridge  into  two  buccal  cusps,  while 
the  lingual  groove  (n)  runs  to  and  over  the  lingual  marginal 
ridge,  dividing  it  also  into  two  lingual  cusps.  The  two 
divide  the  tooth  from  buccal  to  lingual,  into  nearly  equal 
parts.  The  mesial  portion  is  usually  slightly  the  larger. 
The  four  grooves  form  a  cross  through  the  occlusal  surface, 
dividing  it  into  four  lobes,  or  developmental  parts,  on  each 
of  which  there  is  a  cusp  and  a  triangular  ridge.  In  some 
examples  the  grooves  do  not  exactly  meet  at  the  central  pit. 
The  lingual  may  rise  to  the  mesial  of  the  buccal,  or  vice 
versa  ;  or,  a  similar  variation  may  occur  in  the  central  ends 
of  the  mesial  and  distal,  causing  irregularity  of  the  contour 
of  the  central  fossa.  Occasionally,  the  lobes  are  of  unequal 
size,  or  the  cusps  are  unequally  developed,  giving  rise  to  im- 
perfect forms  (Fig.  84). 

112.  On  the  average,  the  cusps  of  the  lower  second 
molar  are  higher  and  more  pointed,  and  the  triangular  ridges 
are  more  prominent  than  in  the  first  molar.  The  mesio-buc- 
cal  and  mesio-lingual  cusps  are  generally  a  little  larger  than 
the  disto-buccal  and  disto-lingual ;  also,  the  mesio-buccal 
and  mesio-lingual  triangular  ridges  (Fig.  83,  ^,  i)  are  usu- 
ally more  prominent.  The  crests  of  these  ridges  do  not  run 
directly  toward  the  central  pit,  but  the  two  mesial  ones  meet 
mesially  of  the  central  pit,  while  the  two  distal  meet  distally 


92  ..  THE    LOWER    SECOND    MOLAR. 


of  it.  When  they  are  liigli,  they  form  transverse  ridges  by 
their  junction,  which  separate  a  mesial  and  a  distal  supple- 
mental fossa  from  the  central  fossa.  When  this  occurs,  there 
are  usually  triangular  supplemental  grooves  deflected  from 
the  mesial  and  distal  grooves,  to  the  mesial  and  distal  of  the 
triano-ular  ridges,  which  run  toward  the  ano-les  of  the  tooth 
and  sej)arate  the  triangular  from  the  marginal  ridges,  widen- 
ing and  deepening  the  supplemental  fossae.  A  deep  pit  is 
often  found  at  the  point  where  these  triangular  grooves  arise 
from  the  principal  grooves.  Supplemental  fossse  occur  much 
more  frequently,  or  are  more  pronounced,  in  the  mesial  than 
in  the  distal  portion  of  the  tooth,  but  in  many  examples  the 
triangular  ridges  are  so  widely  divided  by  sulcate,  mesial 
and  distal  grooves  that  no  supplemental  fossje  are  seen. 

113.  In  some  examples  the  lower  second  molar  presents 
differences  in  the  comparative  size  of  its   lobes,  and   the 

'grooves  may  be  deflected  from  their  normal  course.  Occa- 
sionally, the  distal  groove  is  divided,  and  passes  over  the 
distal  marginal  ridge  in  two  divisions,  with  a  small  tubercle 
between  them.  In  poorly-developed  teeth  there  may  be 
many  supplemental  grooves,  or  wrinkles,  running  from  the 
developmental  grooves  np  onto  the  central  inclines  of  the 
ridges  and  cusps. 

114.  Fissures  occur  oftenest  near  the  central  ends  of 
the  grooves ;  though  they  may  appear  in  any  part  of  their 
length ;  and  in  poorly-developed  teeth  the  sujDplemental 
grooves  may  be  deeply  fissured. 

115.  The  buccal  surface  of  the  lower  second  molar 
(Fig.  85)  is  convex  in  all  directions,  except  that  it  is  partially 
divided  into  two  sections,  or  ridges,  by  the  buccal  groove  (c), 
which  runs  over  onto  it  from  the  occlusal  surface.  In 
many,  this  groove  ends  near  the  center  of  the  surface  in  a 
deep  buccal  jDit  {d).  This  tooth  has  no  disto-buccal  groove. 
The   mesial   and   distal   margins   converge  less  toward  the 

■  gingival  line  than  they  do  in  the  lower  first  molar.     The 


,   THE    LOWER    THIRD   MOLAR.  93 

gingival  line  is  nearly  straight,  and  there  is  a  strong  inclina- 
tion of  the  border  of  the  enamel  toward  it,  giving  the  appear- 
ance of  a  gingival  enamel  ridge. 

116.  *The  lingual  surface  (Fig.  86)  is  similar  in  all  points 
to  that  of  the  lower  first  molar  (7,  v.^  Par.  105);  but,  on 
account  of  a  much  less  convergence  of  the  mesial  and  distal 
surfaces  toward  the  lingual,  this  surface  is  nearly  as  large  as 
the  buccal  surface. 

117.  The  mesial  surface  (Fig.  87)  of  the  lower  second 
molar  is  generally  a  little  more  convex  than  in  the  lower 
first  {q.  v.^  Par.  106) ;  but  in  other  respects  they  are  similar. 

118.  The  distal  surface  (Fig.  88)  differs  from  that  of 
the  lower  first  molar  in  not  having  the  distal  protuberance 
due  to  the  fifth  cusp.  Its  proximating  point  with  the  tooth 
distal  to  it  is  usually  central,  or  toward  the  lingual,  instead 
of  the  buccal  margin,  as  in  the  lower  first  molar.  This  sur- 
face is  usually  quite  regularly  and  smoothly  convex,  and  its- 
gingival  line  seldom  shows  any  bucco-lingual  curvature. 

119.  The  roots  of  the  lower  second  molar  (Figs.  85  to 
89)  are  similar  to  those  of  the  first  molar ;  but  the  divisions 
are  much  less  spread  and  less  grooved  on  the  mesial  and 
distal  sides.  In  many  examples  there  is  but  a  single  root, 
which  is  deeply  grooved  on  its  buccal  and  lingual  sides, 
marking  out  the  divisions.  The  root  is  much  more  irreo-u- 
lar  in  form  than  in  the  lower  first  molar,  and  is  often  much 
curved  distally  (Fig.  89)  or  otherwise  distorted. 

THE  LOWER  THIRD  MOLAR. 

120.  The  lower  third  molar,  called  also  the  wisdom 
tooth  or  Dens  Sapientia,  is  the  eighth  from  the  median  line, 
and  the  last  tooth  in  the  arch.  It  proximates  the  lower 
second  molar  by  its  mesial  surface.  The  tooth  has  two 
typical  forms;  the  one  is  a  four-cusped  tooth,  similar  to  the 
lower  second  molar  (Fig.  83);  the  other  a  five-cusped  tooth, 
similar  to  the  lower  first  molar  (Fig.  75) ;  but  there   are 


94  THE    LOWER    THIRD    MOLAR. 

great  variations  from  both  of  these.  Indeed,  within  the 
observation  of  the  author  the  form  of  this  tooth  is  oftener 
distorted  than  any  other. 

121.  The  four-lobed  tooth  is  the  more  common  form, 
and,  when  well-developed,  the  occlusal  surface  is  similar  to 
that  of  the  lower  second  molar.  A  supplemental  fossa  is 
often  seen,  formed  b}^  the  prominence  of  the  mesio-buccal 
andmesio-lingual  triangular  ridges  ;  but  in  the  distal  portion 
of  the  crown  such  a  fossa  rarely  appears.  Indeed,  in  the 
four-cuspid  lower  third  molars,  the  distal  lobes  are  generally 
much  smaller  than  the  mesial  lobes. 

122.  The  course  of  the  grooves  is  often  much  distorted, 
so  that  their  central  ends  fail  to  proximate,  as  in  Fig.  90, 
or  otherwise.  This  renders  the  form  of  the  central  fossa 
extremely  irregular.  Or  the  principal  grooves  may  be  so 
confused  among  a  number  of  supplemental  grooves  that  the 
real  dividing  lines  of  the  lobes  can  scarcely  be  made  out 
(Fio-.  91).  In  many  of  these,  some  of  the  supplemental 
grooves  run  over  the  marginal  ridges,  corrugating  them,  or 
dividino-  them  into  several  imperfect  cusps.  Occasionally 
the  marginal  ridges  are  nearly  equal  in  height  all  around  the 
margin  of  the  central  fossa,  and  the  enamel  surface  of  the 
latter  is  covered  with  small  wrinkles,  some  of  which  may  be 
deeply  fissured. 

123.  In  some  instances  the  lower  third  molar  is  very 
larcre,  and  in  these  the  ridges  may  be  subdivided  into  six, 
seven,  or  eight  cusps,  and  as  many  fairly  distinct  lobes  ;  or, 
one  or  more  supplemental  ridges  may  appear  within  the 
limits  of  the  central  fossa  surrounded  by  grooves,  which 
divide  them  from  other  parts  of  the  crown  (Fig.  92).  Such 
teeth  are  usually  poorly  formed,  and  the  grooves  deeply 
fissured. 

124.  The  five-lobed  lower  third  molars  are  very  large 
teeth,  larger  than  the  second  molars,  and  very  regularly 
formed.     The  distal  lobe  is  placed  further  to  the  distal  and 


0^  .^^-^-^^ 


Fig.  91. 


Fig.  92. 


Fig.  93. 


Fig.  94. 


Fig.  95. 


Fig.  90*  (Par.  122).— Left  Lower  Third  Molar,  Occlvsal  Soeface,  imperfect  foiTa. 
<j,  Mesio-buccal  cusp ;  h,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ; 
e,  mesial  marginal  ridge  ;  /,  distal  marginal  ridge  ;  fj,  mesial  groove  ;  U,  buccal  groove  ; 
i,  lingual  groove ;  A-,  distal  groove.  The  buccal  and  lingual  grooves  do  not  meet  in  the 
central  fossa  as  in  regular  forms. 

Fig.  91*  (Par.  122).— Lower  Third  Molar,  Occlusal  Surface,  verj-  imperfect  form, 
a,  INIesio-buccal  cusp  ;  &,  disto-buceal  cusp  ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual  cusp  • 
e,  mesial  marginal  ridge  ;  /,  distal  marginal  ridge  ;  g,  mesial  groove ;  h,  buccal  groove  ; 
i,  lingual  groove  ;  k,  distal  groove.  Several  of  the  grooves  are  fissured  and  are  irregular  in 
form. 

Fig.  92*  (Par.  123).— Right  Lower  Third  Molar,  Occlus.^l  Surface,  very  large  and 
irregular  in  form,  a,  Mesio-buccal  cusp ;  h,  a  very  imperfect  cUsto-buccal  cusp ;  c,  mesio- 
lingual  cusp,  with  a  sharp,  triangular  ridge,  running  very  much  to  the  distal ;  d,  disto- 
lingual  cusp,  standing  very  much  to  the  medial  of  its  proper  position ;  e,  /,  a  large 
supplemental  ridge,  occupying  the  middle  portion  of  the  central  fossa  v  g,  mesial  mar- 
ginal ridge  ;  h,  distal  marginal  ridge ;  i,  mesial  groove,  deeply  fissured  and  with  supple- 
mental grooves,  also  fissured,  extending  to  the  labial  and  lingual,  forming  a  supplemental 
mesial  fossa  ■  k,  buccal  groove  ;  I,  lingual  groove  ;  m,  n,  deep  fissure  on  either  side  of  the 
supplemental  ridge.  There  are  a  number  of  deep  wrinkles  running  over  the  distal  mar- 
ginal ridges. 

Fig.  93*  (Par.  12.5).— Right  Lom'er  Third  Molar,  Buccal  Surface,  with  five  cusps. 
a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  buccal  groove ;  d,  buccal  pit ;  e,  disto- 
buccal  groove ;  /,  distal  cusp;  g,  gingival  line;  h,  mesial  root;  i,  distal  root.  In  this 
tooth  the  distal  root  is  the  larger,  and  the  two  come  together  at  their  apexes,  each  of 
which  is  unusual. 

Fig.  91*  (Par.  127).— Right  Lower  Third  Molar,  with  the  roots  curved  very  much 
to  the  distal. 

Fig.  95*  (Par.  127). -Left  Lower  Third  Molar,  Buccal  Surface;  three  roots,  a, 
Mesio-buccal  cusp ;  b,  disto-buccal  cusp ;  c,  distal  cusp ;  d,  buccal  groove ;  /,  gingival 
line  ;  g,  mesial  root ;  h,  distal  root ;  i,  supernumerary  root. 


*  Illustration,  V/i  diameters. 


THE    DECIDUOUS    TEETH.  97 

lingual,  and  the  buccal  surface  is  more  rounded  than  in  the 
lirst  molars.     This  form  is  bilateral  and  hereditary. 

125.  The  buccal  surface  of  the  lower  third  molar  (Figs. 
93,  94,  95)  is  usually  more  convex  than  in  the  other  lower 
molars,  but  otherwise  of  the  same  form.  If  four-lobed,  this 
tooth  has  the  same  grooves  and  pits  as  the  lower  second  ;  if 
five-lobed,  it  has  the  markings  of  the  lower  first  molars. 

126.  The  mesial,  lingual,  and  distal  surfaces  corre- 
spond with  those  of  the  other  lower  molars,  only  rather  more 
rounded  ;  especially  the  distal,  which  is  often  nearly  a  true 
circle  from  buccal  to  lingual. 

127.  The  root  of  the  lower  third  molar  (Figs.  93,  94, 
95),  as  compared  with  its  crown,  is  usually  much  smaller 
than  in  the  other  lower  molars.  It  may  be  single,  or  divided 
into  two  or  more  prongs,  the  tendency  being  to  the  forma- 
tion of  two  roots,  the  same  as  in  the  other  lower  molars ; 
and  much  the  greater  number  have  the  root  in  this  form, 
though  the  single  root  is  common,  and  three  roots  (the 
mesial  being  divided)  are  not  rare.  The  root,  or  roots,  of 
this  tooth  usually  curvd'  distally,  sometimes  very  much,  and 
are  otherwise  distorted.  In  extracting,  this  inclination  of 
the  roots  should  be  kept  in  mind. 

THE  DECIDUOUS  TEETH. 

128.  These  are  the  teeth  of  early  childhood,  and  serve 
for  mastication  till  the  maxillary  bones  are  sufficiently  de- 
veloped to  accommodate  the  permanent,  the  larger  teeth  of 
adult  age.  They  are  then  removed  by  absorption  of  their 
roots,  which  allows  their  crowns  to  fall  away.  Kence  they 
are  often  called  temporary  teeth.  The  shedding  process  be- 
gins about  the  seventh  year,  and  is  completed  at  from  the 
twelfth  to  the  fourteenth,  the  succedaneous  teeth  taking  the 
places  of  the  deciduous.  There  are  twenty  deciduous  teeth  ; 
ten  in  each  jaw,  namely :  two  central  incisors,  two  lateral 
incisors,  two  cuspids,  and  four  molars.  This  may  be  ex- 
pressed by  the  following  formula: 

H 


98  THE    DECIDUOUS    TEETH. 

1 1  C  I  M  I  =20 
There  are  no  bicuspids  in  the  deciduous  set,  and  therefore 
the  deciduous  first  molars  proximate  directly  ^Yith  thetlecid- 
uous  cuspids.     The  bicuspids  of  the  j^ermanent  set  are  suc- 
cedaneous  to  the  deciduous  molars. 

129.  The  incisors  and  cuspids  of  the  deciduous  set  are 
(Fio;s.  96  to  101)  similar  in  form  and  lobal  construction  with 
their  succedaneous  teeth,  but  the  deciduous  molars  give  place 
to  the  permanent  bicuspids,  which  are  of  very  dissimilar 
pattern.  The  deciduous  second  molars  (Fig.  103, 105),  both 
upper  and  lower  are  of  the  same  form  and  lobal  construction 
as  the  permanent  first  molars.  The  deciduous  first  molars, 
upper  and  lower,  have  no  similar  teeth  in  the  permanent  set. 
Their  form,  and  the  arrangement  of  their  lobes  are  peculiar 
to  themselves.  Therefore  the  crowns  of  these  will  be  sepa- 
rately described.     (Pars.  134  to  150.) 

130.  Though  the  crowns  of  the  temporary  teeth  are, 
with  the  exceptions  mentioned,  of  similar  form  and  lobal 
construction  as  the  permanent,  there  are  certain  minor  differ- 
ences which  distinguish  them.  The}'  are  considerably  smaller 
than  the  corresponding  permanent  teeth.  This  reduction  in 
size  includes  the  Avhole  tooth,  and  is  such  that  it  leaves  the 
general  proportions  unchanged,  except  that  the  roots  are  pro- 
portionally longer. 

131.  The  deciduous  teeth  are,  however,  marked  with  a 
much  greater  constriction  at  their  necks.  The  enamel,  in- 
stead of  thinning  away  to  the  gingival  border  as  in  the  per- 
manent teeth,  retains  its  thickness  almost  to  the  gingival 
line  and  terminates  abruptly,  leaving  a  sudden  constriction 
of  the  neck  of  the  tooth.  This  varies  in  degree,  but  is  com- 
mon to  all  of  the  deciduous  teeth,  and  distinguishes  them 
from  the  permanent  teeth. 

132.  The  buccal  and  lingual  surfaces  of  the  deciduous 
molars  are  inclined  toward  the  occlusal  surface  much  more 
than  those  of  the  permanent,  so  that  the  immediate  occlusal 


Fm   90  Fig.  97.  Fig.  98. 


Fig.  99.  Fig.  100.  Fig.  101. 


Fig.  104. 


Fig.  105. 


Fig.  106. 


Fig.  107 


Fig.   96*  (Par.  129).— Deciduous  Upper  Central  Iscsor. 

Fig.   97*  (Par.  129).— Deciduous  Upper  Lateral  Incisor. 

Fig.    98*  (Par  129).— DECiDUors  Upper  Cuspid. 

Fig.   99*  (Par.  129).— Deciduous  Lower  Central  incisoe. 

Fig.  100*  (PsLT.  129).— Deciduous  Lower  Laterial  Incisoe. 

Fig.  101*  (Par.  129).— Deciduous  Lower  Cuspid. 

Fig.  102*  (Par.  138).— Left  Upper  First  Deciduous  Molar,  Buccal  Surface,  a, 
Bui  co-gingival  ridge  ;  b,  mesio-buccal  cusp ;  c,  disto-buccal  cusp ;  d,  buccal  ridge  ;  e, 
buccal  groove. 

Fig.  103*  (Par.  129).— Left  ITrper  Second  Deciduous  Molar. 

Fig.  104*  (Par.  148).— Left  Lower  First  Deciduous  Molar,  Buccal  Surface,  a, 
Bucco-gingival  ridge  ;  b,  mesio-buccal  cusp ;  c,  disto-buccal  cusp ;  d,  buccal  ridge  ;  e, 
buccal  groove. 

Fig.  105*  (Par.  129).— Left  Lower  Second  Deciduous  Molar,  Buccal  Surface. 

Fig.  106*  (Par.  141).— Lower  First  and  Second  Deciduous  Mol.ars,  Occlusal  Sur- 
faces. The  lobes  and  grooves  of  ttie  lower  second  deciduous  molar  are  the  same  as  those 
of  the  permanent  lower  first  molar,  Fig.  75.  The  lower  deciduous  first  molar  has  four 
lobes,  a,  Jlesial  groove ;  b,  buccal  groove ;  c,  lingual  groove :  d,  distal  aroove  ;  c,  mesio- 
buccal  cusp  ;  /,  disto-buccal  cusp  ;  g,  mesio-lingual  cusp ;  //,  disto-lingual  cusp  ;  (,  mesial 
fossa. 

Fig.  107*  (Par.  134).— L^ft  Upper  First  and  Second  Deciduous  Molars.  The  second 
deciduous  molar  has  its  grooves  and  lobes  in  the  same  form  as  those  ot  the  first  perma- 
nent molar.  Fig.  54.  The  upper  first  deciduous  molar  has  but  three  cusps,  a,  Mesial 
groove  ;  b,  distal  groove  ;  c,  buccal  groove  ;  d,  mesio-buccal  cusp ;  (,  disto-buccal  cusp  :  /, 
lingual  cusp. 


=  Illustration,  lyi  diameters. 


UPPER    FIRST   DECIDUOUS   MOLAR.  101 


surface  is  narrow  in  proportion  to  the  greatest  bucco- 
lingual  thickness  of  the  crown.  This  gives  the  crown  as 
seen  in  the  mouth  the  appearance  of  being  very  long  from 
mesial  to  distal ;  though  this  characteristic  is  less  marked  in 
the  upper  than  in  the  lower  deciduous  molars  (see  FWs.  106 
and  107). 

133.  The  enamel  of  the  deciduous  teeth  is  usually 
whiter  than  that  of  the*permanent  teeth,  and  they  are  proba- 
bly of  coarser  texture.  The  difference  in  color  is  often 
strongly  contrasted  when  some  of  the  permanent  teeth,  as  the 
centra]  incisors,  have  taken  their  places  by  the  side  of  the 
remaining  temporary  teeth. 

UPPER    FIRST    DECIDUOUS    MOLAR. 

134.  The  occlusal  surface  of  the  upper  first  decidu- 
ous molar  (Fig.  107)  when  seen  in  the  line  of  the  long  axis 
of  the  tooth,  presents  an  irregular  quadrangular  form  in 
which  the  buccal  marginal  line  is  the  longest"  The  mesio- 
buccal  angle  is  acute,  the  mesio-lingual  is  obtuse,  and  both 
distal  angles  are  nearly  right  angles.  The  buccal  margin  is 
irregularly  convex,  and  the  lingual  margin  regularly  rounded. 
Both  the  buccal  and  the  lingual  surfaces  are  much  inclined 
centrally,  or  toward  the  occlusal  surface. 

135.  This  tooth  has  three  lobes,  divided  by  three 
grooves.  The  mesial  (a)  and  distal  (b)  grooves  rim  from  the 
mesial  to  the  distal  margin  in  a  deep  sulcus,  and  divide  the 
lingual  from  the  buccal  lobes.  Their  junction  is  in  a  pit  in 
the  central  fossa.  The  buccal  groove  (c)  rises  from  the  same 
pit,  at  the  junction  of  the  mesial  and  distal  grooves,  and 
runs  over  the  buccal  marginal  ridge  to  the  buccal  surface. 
This  groove  is  generally  without  a  sulcus;  or,  at  most,  there 
is  but  a  slight  furrow. 

136.  The  buccal  marginal  ridge  is  a  high  cutting  edge 
which  rounds  up  from  the  mesio-buccal  angle  of  the  occlusal 
surface  and  runs  to  the  distal  and  buccal  till  it  reaches  the 


102  ,  UPPER    FIRST    DECIDUOUS   MOLAR. 

point  of  the  mesio-buccal  cusp  (d).  Its  direction  is  then  to 
the  distal,  descending  slightly  to  the  buccal  groove,  then 
horizontally  to  the  disto-buccal  angle  to  join  the  distal  mar- 
ginal ridge,  the  latter  portion  forming  a  small  disto-buccal 
cusp  (e).  In  unworn  teeth,  the  buccal  groove  causes  a  marked 
but  slight  depression  where  it  crosses  the  ridge,  breaking  it 
into  t.Avo  cusps;  the  mesial  being  the  larger  and  more  pointed; 
This  division  is  generally  defaced  veiy  early  by  wear,  so  that 
the  ridge  presents  an  almost  straight  rounded  edge. 

137.  The  lingual  cusp  (/)  is  in  the  form  of  an  elevated 
crescentic  edge  with  its  convexity  to  the  lingual,  which  runs 
from  the  mesial  termination  of  the  mesial  groove  (a)  to  the 
distal  termination  of  the  distal  groove  (6).  The  central  and 
the  lingual  inclines  of  this  cusp  are  nearly  equal  slopes,  while 
the  buccal  incline  toward  the  buccal  marginal  ridge  is  less 
abrupt  than  the  central.  The  mesial  and  distal  marginal 
ridges  are  not  marked  by  more  than  a  very  slight  thickening 
of  the  enamel,  and  arc  cat  through  by  the  mesial  and  distal 
grooves. 

138.  The  buccal  surface  (Fig.  102)  is  remarkable  for  its 
bucco-gingival  ridge  (a),  which  stands  boldly  out  from  the 
gingival  line  from  oue  to  three  millimeters  and  extends  from 
the  mesio-buccal  to  the  disto-buccal  angle  of  the  tooth.  At 
the  mesio-buccal  angle  it  terminates  abruptly  in  a  marked 
prominence,  and  diminishes  gradually  as  it  passes  to  the 
disto-buccal  angle. 

139.  From  the  summit  of  the  bucco-o-ino-ival  rido;e  to 
the  summit  of  the  buccal  marginal  ridge,  or  the  mesio-buccal 
cusp,  is  nearly  a  flat  surface,  except  a  slight  depression  along 
the  buccal  groove.  In  many  examples  there  is  a  slight  con- 
cavity extending  from  mesial  to  distal  along  the  occlusal 
margin  of  the  bucco-gingival  ridge,  and  from  the  point  of  the 
mesio-buccal  cusp  a  strong  ridge  runs  to  the  mesio-buccal 
prominence  of  the  bucco-gingival  ridge. 

110.     The  mesial  and  distal  surfaces  are  quite  smoothly 


LOWER    FIRST    DECIDUOUS    MOLAR.  103 

flattened.     The  lingual  surface  is  convex.     The  neck  presents 
the  characteristic  constriction  common  to  deciduous  teeth. 

LOWER    FIRST    DECIDUOUS   MOLAR. 

141.  The  occlusal  surface  of  the  lower  first  deciduous 
molar  (Fig.  106),  when  viewed  in  a  line  with  the  long  axis 
of  the  tooth,  presents  the  outline  of  a  parallelogram,  modified 
by  the  rounding  of  its  angles  and  more  or  less  convexity  of 
its  lines.  In  many,  the  distal  portion  is  broader  than  the 
mesial,  giving  the  tooth  an  ovoid  outline.  There  are  two 
fossae.  The  principal  fossa  occupies  nearly  three-fourths  of 
the  distal  portion  of  the  surface,  while  the  small  mesial  fossa 
occupies  the  immediate  mesial  portion. 

142.  The  tooth  has  four  lobes  of  irregular  form,  divided 
by  four  grooves.  These  grooves  all  run  from  the  principal 
fossa.  The  mesial  groove  (rt,  a)  rises  from  the  central  pit  and 
runs  to  the  mesial,  passing  over  the  transverse  ridge  into  the 
mesial  fossa,  where  it  is  deflected  sharplj'  to  the  lingual, 
passing  over  the  marginal  ridge  near  the  mesio-linguo-occlusal 
angle.  This  groove  varies  considerably  in  its  course  in  dif- 
ferent examples.  In  the  principal  fossa  it  usually  inclines  to 
the  buccal  and  then  toward  the  lingual,  but  there  is  generally 
an  angle  at  the  origin  of  the  buccal  groove.  The  buccal 
groove  {b)  rises  from  the  mesial  groove,  some  distance  to  the 
mesial  of  the  pit,  and  runs  over  the  buccal  ridge  on  to  the 
buccal  surface,  in  a  slight  sulcus,  dividing  the  buccal  mar- 
ginal ridge  into  two  cusps,  the  mesio-  and  disto-buccal.  Its 
position  determines  the  relative  size  of  thfe  buccal  lobes.  The 
lingual  groove  (c)  runs  from  the  central  pit' over  the  lingual 
marginal  ridge  on  to  the  lingual  surface,  and  is  deeply  sulcate 
on  the  central  incline  of  the  ridge.  The  distal  groove  {d) 
arises  from  the  central  pit  and  runs  over  the  distal  marginal 
ridge  nearly  centrally,  to  the  distal  surface.  It  is  often  de- 
flected to  the  buccal  in  the  flrst  part  of  its  course  by  the  point 
of  the  disto-lino;nal  triangular  rido-e. 


104  LOWER    FIRST^DECIDUOUS    MOLAE. 

143.  This  tooth  has  four  cusps  corresponding  with  tlie 
four  lobes.  The  mesio-huccal  lobe  (e)  is  very  irregular  in  its 
outline.  It  forms  the  entire  mesial  marginal  ridge,  and  from 
one-third  to  three-fourths  of  the  slopes  of  the  mesial  fossa- 
The  mesial  marginal  ridge  is  usuall}'  high  in  j^oung,  unworn, 
teeth.  It  is  curved,  and  from  the  mesio-bucco-occlusal  angle 
of  the  tooth  it  becomes  the  buccal  maro-inal  rido;e,  and  rises 
to  the  distal  to  form  the  point  of  the  mesio-buccal  cusp  (e)- 
From  the  point  of  the  cusp  it  falls  away  to  the  distal  and 
buccal  to  the  buccal  groove.  A  prominent  triangular  ridge 
descends  from  this  cusp  to  the  lingual  and  distal,  and  joins  a 
similar  triangular  ridge  from  the  mesio-lingual  cusp  (g)  to 
form  the  transverse  ridge,  thus  dividing  the  mesial  from  the 
principal  fossa.  Exceptionally,  a  deep  sulcus  divides  these 
triangular  ridges  and  connects  the  fossae.  From  the  buccal 
groove,  the  bucaal  marginal  ridge  passes  almost  directly  to 
the  disto-bucco-occlusal  angle  where  it  joins  the  distal  luar- 
ginal  ridge.  In  the  central  portion  it  rises  slightly  to  form 
the  low  disto-buccal  cusp  (/).  The  triangular  ridge  from 
this  cusp  is  usually  low,  or  wanting. 

144.  The  lingual  marginal  ridge  (^,  h)  rises  abruptly 
from  the  mesial  groove  to  the  summit  of  the  mesio-lingual 
cusp  (_^),  and  then  falls  away  toward  the  distal  and  lingual 
to  the  lingual  groove.  In. most  specimens,  in  unworn  teeth, 
the  mesio-lii]gual  cusp  is  sharp,  and  its  point  is  carried  by 
the  lingual  incline  far  toward  the  central  line  of  the  tooth, 
so  much  so  as  to  be  in  marked  contrast  with  the  general  form 
of  the  lingual  cusps  ^f  the  lower  molars.  From  its  apex  a  tri- 
angular ridge  descends  to  join  that  from  the  mesio-buccal  cusp 
in  forming  the  transverse  ridge.  From  the  lingual  groove, 
the  lingual  marginal  ridge  rises  to  the  point  of  the  disto- 
lingual  cusp  (A)  and  then  falls  away  in  a  curve  to  form  the 
distal  marginal  ridge.  This  cusp  is  generally  rather  low,  but 
varies  much  in  these  teeth.     In  some  cases  there  is  a  sharp 


LOWER   FIRST   DECIDUOUS   MOLAR.  105 

triangular  ridge  descending  into  the  central  fossa,  but  more 
generally  this  ridge  is  slight. 

145.  The  distal  marginal  ridge  is  usually  made  to  ap- 
pear prominent  by  the  depth  of  the  principal  fossa.  It  is 
crossed  near  its  center  by  the  distal  groove. 

146.  The  principal  fossa  is  generally  deep  and  well 
rounded.  The  distal  triangular  ridges,  the  only  ones  descend- 
ing into  this  fossa,  are  generally  not  prominent,  but  occasion- 
ally they  are  sufficiently  so  to  render  the  fossa  very  angular. 
I  have  observed  many  in  which  the  enamel  in  this  fossa 
was  very  imperfect  and  the  bottom  of  the  fossa  broad  and 
rough. 

147.  The  mesial  fossa  (z)  is  usually  sharp  and  deep,  with 
smooth  inclines,  and  has  a  central  pit  that  is  frequently  the 
seat  of  caries. 

148.  The  buccal  surface  of  the  lower  first  deciduous 
molar  (Fig.  104)  is  remarkable  for  its  prominent  bucco-gin- 
gival  ridge  («),  which  runs  from  the  mesial  to  the  distal 
margin  and  stands  out  prominently  over  the  junction  of  the 
crown  with  the  root.  From  mesial  to  distal,  this  ridge 
slopes  toward  the  occlusal  surface,  making  the  crown  longer 
at  the  mesio-buccal  angle  than  at  the  disto-buccal.  From 
this  ridge  the  surface  slopes  rapidly  toward  the  occlusal 
margin,  and  more  rapidly  at  the  mesial  than  the  distal  por- 
tion. From  the  mesio-buccal  cusp  a  strong  ridge  of  enamal 
runs  to  the  more  prominent  portion  of  the  bucco-gingival 
rido;e  near  the  mesio-buccal  angle,  of  the  tooth.  Otherwise 
liis  surface  is  nearly  flat.  The  lingual  surface  is  usually 
well  rounded,  but  is  broken  toward  the  occlusal  surface  by 
the  prominence  of  the  mesio-lingual  cusp,  and  the  sulcus  of 
the  lingual  groove. 

149.  The  mesial  and  distal  surfaces  are  slightly 
rounded.  The  disto-buccal  and  disto-lingual  angles  of  the 
tooth  are  about  ecpial  in  prominence,  but  the  mesio-buccal 
and  mesio-lingual   angles   are   very   unequal.      The  mesial 


106  THE    PULP   CHAMBER. 


surface  slopes  rapidly  to  the  lingual,  making  the  lingual 
surface  much  shorter,  mesio-distally,  than  the  buccal.  The 
mesio-buccal  angle  is  acute  and  prominent,  while  the  mesio- 
lingual  is  very  obtuse  and  rounded. 

150.  '  The  root  of  this  molar  is  divided  into  two  prongs, 
which  are  spread  widely  apart.  They  are  thin  from  mesial 
to  distal,  and  slightly  grooved ;  and,  from  buccal  to  lingual,, 
broad.  They  taper  regularly  to  broad,  flat  apexes,  which  are 
occasionally  bifurcated  a  short  distance. 

151.  The  roots  of  the  deciduous  teeth  are  the  same  in 
number  and  general  characteristics  as  in  the  teeth  of  the 
same  denomination  in  the  permanent  set,  except  that  those 
of  the  molars  are  more  divergent.  This  spreading  of  the  roots 
accommodates  the  crowns  of  the  permanent  bicuspids,  which 
are  developed  between  the  roots  of  the  deciduous  molars. 
Those  of  the  lower  jaw  are  thin  from  mesial  to  distal,  broad 
from  buccal  to  lingual,  and  grooved  along  their  flattened  sides. 
The  mesial  and  distal  roots  of  the  upper  deciduous  molars 
are  also  thin,  grooved,  and  widely  divergent.  The  lingual 
root  stands  boldly  to  the  lingual,  forming  a  wide  space  be- 
tween the  three,  for  the  crowns  of  the  upper  bicuspids.  In 
many  examples  the  lingual  and  distal  roots  are  joined  by 
broad  thin  connections  for  the  greater  part  of  their  length. 

THE    PULP    CHAMBER. 

152.  Every  tooth  has  a  cavity  in  the  center  of  the 
crown,  and  one  or  more  canals  extending  through  the  long 
axis  of  the  root,  or  roots,  to  the  apex.  This  cavity  contains- 
a  tissue  composed  of  cellular  elements  imbedded  in  a  semi- 
gelatinous  matrix,  tilling  every  part  of  the  space,  and  is 
richl}^  supplied  with  blood-vessels  and  nerves.  This  is  known 
as  the  pulp  of  the  tooth.* 

*  As  the  form  of  the  pulp  chamber  gives  the  exact  form  of  the  pulp,  no- 
separate  description  of  the  pulp  will  be  given.  It  is  not  my  purpose  to  give 
any  histological  descriptions  in  this  work. 


THE    PULP   CHAMBER.  107 


153.  The  central  cavity  in  the  tooth  is  usually  divided 
into  a  crown,  or  coronal  portion,  and  a  root  portion.  Its 
parts  are  familiarly  known  as  the  pulp  chamber  (crown 
cavity),  and  root  canal,  or  root  canals.  The  pulp  chamber  is 
comparatively  large,  and  the  root  canals  are  small,  tapering 
from  the  pulp  chamber  to  a  minute  opening  at  the  apex  of 
the  root,  known  as  the  apical  foramen.  In  those  teeth  that 
have  prominent  cusps,  as  the  bicuspids  and  molars,  there  is 
a  prolongation  of  the  pulp  toward  the  point  of  each  cusp. 
These  are  known  as  the  horns  of  the  pulp  ;  and  the  prolon- 
gations of  the  chamber  are  designated  the  horns  of  the  pulp 
chamber. 

154.  The  size  of  the  pulp  chamber  and  of  the  root 
canals  varies  greatly  in  teeth  of  different  denominations  ; 
and  also  in  different  teeth  of  the  same  denomination.  In  the 
early  formative  stages  of  the  teeth  it  is  very  large,  and 
diminishes  in  size  as  growth  proceeds,  until  the  tooth  is 
fully  formed.  Afterward  this  diminution  goes  on  slowly, 
until,  in  old  age,  it  is  often  nearly  obliterated.  In^the  forma- 
tive stage,  i.  e.,  during  the  growth  of  the  root  of  the  tooth, 
the  root  canal  is  large  and  funnel-shaped,  with  the  open  end 
of  the  funnel  toward  the  apex  of  the  root  (Fig.  72).  As 
growth  proceeds,  and  the  root  approaches  completion,  this 
diminishes  rapidly  till  the  root  is  fully  formed, -Avhen  it  is 
contracted  to  a  small  foramen.  This,  however,  continues  to 
diminish  slowly.  Therefore,  the  size  of  the  pulp  chamber, 
the  root  canals,  and  the  apical  foramen,  are  greater  in  youth 
than  in  old  age.  However,  after  adult  age  is  reached,  the 
diminution  in  size  is  usually  not  great.  During  this  time, 
the  horns  of  the  pulp  chamber  are  shortened  by  the  same 
process  of  formation  of  dentine 'On  their  surface  that  is  going 
on  in  all  parts  of  the  pulp  chamber  and  root  canal.  There- 
fore, the  horns  of  the  pulp  become  shorter,  or  recede,  as  age 
advances.  Indeed,  the  whole  pulp,  very  slowly,  becomes 
smaller. 


108  THE    PULP   OHAMBER. 


155.  Certain  processes,  when  present,  also  serve  to 
diminish  the  size  of  the  pulp  chamber  more  rapidly  ;  especially 
abrasion  of  the  teeth,  a  matter  that  seems  to  depend  largely 
upon  the  character  of  the  occlusion.  When  the  occlusion  is 
such  that  there  is  much  rubbing,  or  sliding  motion,  of  the 
teeth  against  each  other,  wear  goes  on  rapidly.  This  seems 
to  induce  depositions  of  dentine  on  the  walls  of  the  pulp 
chamber,  which  reduces  its  size  ;  and,  especially,  causes  the 
recession  of  the  horns  of  the  pulp.  In  this  way,  exposure  of 
the  pulp  from  the  wearing  away  of  the  dentine  is  delayed  or 
prevented.  In  many  instances  the  pulp  chamber  is  almost 
obliterated  in  the  molars  and  bicuspids,  and  recedes  root- 
wise  of  the  gingival  line  in  the  incisors  and  cuspids.  Slowly 
progressive  caries  or  erosion  of  the  teeth  often  induce  similar 
deposits. 

156.  In  the  incisors  and  cuspids,  the  pulp  chamber  and 
the  root  canal  are  not  sharply  differentiated.  The  latter- 
tapers,  gradually,  from  the  full  size  of  the  largest  crown  por- 
tion to  a  small  foramen  at  the  apex  of  the  root.  In  teeth 
with  more  than  one  root,  the  transition  from  pulp  chamber 
to  root  canal  is  usually  sharply  deiined,  the  former  being 
very  large  as  compared  with  the  pulpal  end  of  the  latter. 
Indeed,  the  general  form  of  the  pulp  is  a  diminished  coun- 
terpart of  the  form  of  the  surface  of  the  tooth,  except  that  it 
is  in  every  way  more  slender. 

157.  Our  studies  thus  far  have  been  of  the  outer  surfaces 
of  the  teeth.  The  pulp  chambers  are  within,  and,  therefore, 
in  the  study  of  them,  dissections  must  be  made  to  expose 
them  to  view.  It  is  often  necessary  for  the  dentist  to  enter 
the  pulp  chambers  of  the  teeth  of  his  j^atients,  and  there  per- 
form delicate  operations  with  a  firecision  which  demands  the 
most  accurate  knowledge  of  these  cavities.  Therefore  this 
work  of  exposure,  and  examination,  of  the  pulp  chambers  of 
teeth  should  be  thorough,  as  a  preparation  for  operations  in 
the  mouth.     The  form  of  dissection  necessary  will  be  given 


Fig.  108. 


Fig-.  109. 


Fitr.  110. 


Fig.  108*  (Par.  160).— The  Pulp  Chamber  of  the  Uppek  Cestr.\l  Incisor,  a,  h, 
Mesio-distal  sections  of  young  teeth,  showing  the  three  short  horns  of  the  pulp  ;  c,  mesio- 
distal  section  of  a  tooth  from  an  adult ;  d,  c,  labio-lingual  sections. 

FiG.  109*  (Par.  160). -Pulp  Chahbek  of  the  Upper  Lateral  Incisor,  a,  b,  Mesio- 
distal  sections ;  c,  labio-lingual  section ;  d,  labio-lingual  section  of  a  very  long  lateral 
incisor. 

Fig.  110"-  (Par.  163).— Pulp  Ch  ^.mber  of  the  Upper  Cuspids,  a,  b,  Mesio-distal  sec- 
tions ;  c,  d,  labio-lingual  sections. 


■Illustration,  actual  size. 


THE    PULP    CHAMBERS   OP    THE   UPPER   INCISORS.  Ill 


ill  connection  with  the  teeth  as  they  are  individually  de- 
scribed. 

THE  PULP  CHAMBERS  OF  THE  UPPER  INCISORS. 

158.  The  pulp  chambers  and  root  canals  of  the  upper 
central  and  lateral  incisors  are  so  similar,  the  description  of 
one  will  do  for  all. 

Dissection. — 1st.  Saw  the  tooth  through  on  the  gingival 
line,  at  the  labial  surface,  at  right  angles  with  the  long  axis. 

2d.  Saw  the  tooth  from  labial  to  lingual,  along  the 
central  line  of  the.  long  axis  from  end  to  end. 

§d.  Saw  the  tooth  from  mesial  to  distal,  along  the 
central  line  of  the  long  axis  from  end  to  end. 

159.  A  very  thin  saw  in  a  strong  frame  should  be 
used,  otherwise  the  lengthwise  dissections  should  be  made  to 
one  side  of  the  central  line  in  the  first  instance,  and  after- 
ward the  whole  length  of  the  pulp  chamber  exposed  by 
grinding  on  a  stone;  or  the  lengthwise  exposure  may  be 
made  by  catching  the  tooth  in  the  vise  and  removing  one- 
half  with  the  file,  or  by  grinding  on  an  emery  wheel.  After 
the  pulp  chamber  is  exposed  so  that  half  of  its  concavity 
remains  in  the  half  of  the  tooth,  and  has  been  ground 
smooth  and  fiat,  it  should  be  inked  on  an  inked  pad  (such  as 
is  used  for  the  rubber  stamps  for  printing),  and  a  print  made 
from  it.  This  will  give  the  form  of  the  tooth  and  pulp 
chamber  in  silhouettes  similar  to  the  accompanying  illus- 
trations. The  printing  is  facilitated  by  sticking  the  tooth  to 
a  piece  of  hard  wax  for  convenience  in  handling.  Ordinary 
modeling  compound,  or  sealing  wax,  is  convenient  and  efifect- 
ive.*  The  printing  is  usually  better  done  by  laying  ordinary 
writing  paper  on  a  sheet  of  semi-soft  rubber,  about  one-eighth 
inch  in  thickness.  This  is  specially  useful  when  the  ground 
surface  cannot  be  perfectly  flat,  as  in  curved  roots. 

*Dr.  Cattell  has  found  that  in  teaching  it  is  very  convenient  to  have  a 
sufficient  number  of  small  pine  blocks  (fxfxl  inch)  to  which  he  has  pupils 
cement  the  teeth  with  sealing  wax. 


112  THE    PULP    CHAMBERS   OF    THE    UPPER    INCISORS. 

160.  In  the  upper  central  and  lateral  incisors  (Figs.  108 
and  109),  there  is  no  distinct  division  of  the  pulp  cavity  into 
pulp  chamber  and  root  canal ;  but  there  is  one  straight  canal, 
from  the  interior  of  the  body  of  the  crown  to  the  apex  of 
the  root,  of  which  the  crown  portion  is  the  larger.  In  young 
teeth,  this  has  very  distinctly  the  form  of  the  surface  of  the 
tooth  and  root,  except  that  it  is  much  more  slender.  The 
largest  diameter  of  the  cavity  is  about  level  with  the  gingi- 
val line  on  the  labial  surface.  From  this  point,  the  pulp 
chamber,  or  canal,  extends  toward  the  cutting  edge  of  the 
tooth,  about  two- thirds  the  length  of  the  crown,  sometimes 
a  little  more,  often  less,  and  ends  in  a  thin  edge,  broad  from 
mesial  to  distal.     In  young  teeth  this  edge  has  three  short 

.horns  (Fig.  108,  «,  b)^  or  prolongations,  extending  toward  the 
three  small  cusps,  or  maramelons,  seen  on  the  edge  of  unworn 
incisors  (21). 

161.  From  the  level  of  the  gino-ival  line  toward  the 
apex  of  the  root  it  taj^ers  very  gradually  and  regularly  to  a 
narrow  canal.  Just  within  the  apex  of  the  root,  almost  at 
the  end,  there  is  usuall}'  a  sudden  contraction  of  the  diameter 
of  the  canal,  lessening  it  from  one-third  to  one-half.  This  is 
the  apical  foramen ;  but  this  contraction  of  the  canal  is  not 
usually  present  for  one  or  two  years,  or  more,  after  the  tooth 
has  taken  its  place  in  the  arch  {q.  v.,  Par.  154). 

162.  The  canal  becomes  smaller  from  youth  to  old  age. 
In  incisors  just  taking  their  places  in  the  arch,  I  have  found 
the  diameter  of  the  canal  at  the  gingival  line  to  be  from  one- 
fourth  to  one-third  the  diameter  of  the  neck  of  the  tooth.  In 
early  adult  age,  the  canal  may  be  said  to  average  about  a 
fourth  the  diameter  of  the  neck  of  the  tooth,  ranging  down 
as  age  advances  to  one-fifth,  or  sixth,  and  even  to  one-tenth. 
In  the  lateral  incisor,  the  chamber  and  canal  are  a  little 
smaller  than  in  the  central,  but  larger  in  proportion  to  the 
size  of  the  tooth. 


f  g 


Fis?.  112. 


Fig.  Ill*  (Par.  164).— Pulp  Chamber  of  the  Lower  Central  and  Lateral  Inctsors. 
a,  &,  c,  Labio-Ungual  sections,  showing  differences  of  form  of  the  pulp  chamber  ;  d,  mesio- 
distal  section ;  e,  /,  labio-lingual  sections,  showing  the  more  usual  forms  of  the  pulp 
chamber ;  g,  m^sio-distal  section,  showing  large  pulp  chamber. 

Fig.  112*  (Par.  165).— Pulp  Ch.amber  of  the  Lower  Cuspids,  a,  Labio-lingual  section, 
showing  a  small  pulp  chamber ;  b,  labio-lingual  section,  showing  a  very  large  pulp 
chamber ;  c,  mesio-distal  section. 


*  Illustration,  actual  size. 


UPPER  CUSPID — PULP  CHAMBER  OF  THE  LOWER  INCISORS.  115 
THE  UPPER  CUSPID. 

163.  The  pulp  chamber  and  root  canal  of  the  upper 
cuspid  (Fig.  110)  is  about  the  same  in  form  as  that  of  the 
central  and  lateral  incisors,  except  that  the  coronal  extremity 
has  the  central  horn  much  extended  toward  the  apex  of  the 
cusp  of  the  tooth,  and  the  mesial  and  lateral  horns  are  prac- 
tically absent.  The  canal  is  proportionately  somewhat  smaller. 
However,  this  tooth  is  often  somewhat  flattened  at  the  neck, 
the  long  diameter  being  from  labial  to  lingual.  In  this  case 
the  pulp  canal  at  the  neck,  and  from  thence  toward  the  apex 
of  the  root,  is  also  much  flattened  in  the  same  direction,  but 
is  progressively  rounded  as  the  apex  is  approached.  In  some 
■examples,  the  labio-lingual  diameter  of  the  canal  is  double  the 
mesio-distal.  As  age  advances,  and  the  canal  becomes  smaller, 
the  opening  is  occasionally  reduced  to  a  mere  slit. 

PULP  CHAMBER  OF  THE  LOWER  INCISORS. 

164.  (Fig.  111.)  The  coronal  portion  of  the  pulp 
-chamber  of  the  lower  incisors  is  much  flattened.  At  the 
level  of  the  gingival  line,  the  long  diameter  is  from  labial  to 
lingual.  The  chamber  extends  toward  the  cutting  edge  of 
the  tooth,  about  two-thirds  the  length  of  the  crown,  and  in 
this  extension  its  diameter  is  progressively  diminished  from 
labial  to  lingual,  and  extended  from  mesial  to  distal,  follow- 
ing the  contour  of  the  surface  of  the  tooth,  and  ends  in  a 
thin  edge.  In  young  teeth  this  has  three  short  projections 
toward  the  mammelons  on  the  cutting  edges  of  the  young, 
unworn  teeth.  The  root  has  usually  a  narrow  slit-like  open- 
ing for  the  greater  portion  of  its  length  (c?,  g),  corresponding 
with  the  form  of  the  flattened  roots.  In  many  instances, 
however,  the  root  canal  is  divided  into  two  portions,  or 
canals,  for  a  part  of  its  length  (e,/).  In  the  adult,  these 
canals  are  usually  very  small.  The  point  of  separation  into 
two  canals  is  irregular,  but  is  usually  slightly  root-wise 
from  the*  level  of  the  gingival  line.     It  may  occur  at  about 


116      PULP   CHAMBER    OF    THE   LOWER   CUSPID — BICUSPIDS. 

the  level  of  the  gingival  line,  or  the  canal  may  remain  single 
for  half  the  length  of  the  root,  and  then  he  divided  for  a 
space,  the  two  uniting  again  before  reaching  the  apex.  Gen- 
erally, there  is  hut  one  apical  foramen.  Instances  occur  in 
which  there  are  two,  each  canal  remaining  distinct  to  the 
end.  As  age  advances,  the  canals  of  the  lower  incisors  often 
become  very  minute. 

PULP  CHAMBER  OF  THE  LOWER  CUSPID. 

165.  The  pulp  chamber,  and  the  root  canal  of  the  lower 
cuspid  (Fig.  112)  are  variable  in  size  and  form.  At  the  neck 
of  the  tooth  the  chamber  is  usually  irregularly  flattened, 
with  the  longer  diameter  from  labial  to  lingual,  and  the 
labial  portion  wider  than  the  lingual.  The  coronal  portion 
extends  about  two-thirds  of  the  length  of  the  crown  toward 
the  point  of  the  cusp,  ending  in  a  point,  or  horn,  which  is 
often  very  slender.  The  form  of  the  root  portion  of  the 
canal  depends  on  the  form  of  the  root.  It  is  sometimes 
nearly  round,  but  more  frequently  it  is  sharply  flattened  for 
the  greater  portion  of  its  length,  becoming  more  rounded 
toward  the  apex.  Occasionally,  this  canal  is  divided  for  a 
part  of  the  length  of  the  root.  Also,  the  root  is  sometimes 
divided,  a  very  small  prong  appearing  on  its  lingual  side. 
In  this  there  is  usually  a  very  small  canal  that  is  difficult  to 
enter  with  a  broach.  In  some  lower  cuspids  the  canal  is  very 
small  (a),  in  others,  very  large  (6).  In  a  few  instances  I  have 
seen  it  more  than  one-third  the  diameter  of  the  root  in  the 
adult.  In  this  case  the  diameter  of  the  canal  is  greater  than 
the  thickness  of  the  walls  of  dentine  and  cementum  by  which 
it  is  inclosed.  This  renders  the  pulp  very  liable  to  exposure 
in  excavating  carious  cavities. 

PULP  CHAMBERS  OF  THE  BICUSPIDS. 

166.  Dissections. — 1st.  Divide  the  crown  from  the  root 
on  the  gingival  line  with  a  fine  saw. 


Fig.  115. 


a  b 

Fig.  116. 


Fig.  113*  (Par.  167).— Pulp  Chambkr  and  Root  Canals  of  the  Upper  First  Bicuspids. 
b,  Bucco-lingual  section  of  single-rooted  tooth,  with  single  canal  divided  near  the  apex 
of  the  root ;  a,  cross-section  of  the  same,  mid-length  of  the  root ;  d,  hucco-lingual  section 
of  a  single-rooted  tooth  with  two  canals,  which  connect  at  one  point ;  c,  cross-section  of 
the  same,  a  little  rootwise  from  the  pulp  chamber ;  e,  bucco-lingual  section  of  a  double- 
rooted  tooth,  showing  the  more  usual  form  of  the  chambers  and  canals. 

Fig.  114*  (Par.  168).— Pulp  Chamber  axd  Root  Canals  of  the  Upper  Second  Bi- 
cuspid, a,  Bucco-lingual  section,  showing  chamber  with  a  long,  slender  horn,  also  two 
canals,  which  unite  in  the  apical  third  of  the  root ;  b,  cross-section  of  a  root  with  two 
canals ;  c,  cross-section  of  a  root  with  a  single  large  canal ;  d,  bucco-lingual  section  of  a 
single  root  with  two  canals ;  e,f,  bucco-lingual  sections,  showing  the  more  usual  form  of 
the  pulp  chamber  and  root  canal  of  this  tooth. 

Fig.  115*  (Par.  169).— Pulp  Chamber  and  Root  Canals  of  the  Lower  First  Bi- 
cuspid, a,  Bucco-lingual  section,  showing  the  more  usual  form  ;  b,  bucco-lingual  section, 
showing  a  peculiar  and  very  unusual  division  of  the  root  canal ;  c,  cross-section  in  the 
body  of  root. 

Fig.  116*  (Par.  169).— Pulp  Ch.4:mber  and  Root  Canal  of  the  Lower  Second  Bi- 
cuspid, a,  b,  Bucco-lingual  sections,  showing  the  more  usual  forms  of  the  chamber  and 
canal  in  this  tooth. 


*  Illustration,  actual  size. 


PULP   CHAMBER   OF   THE   UPPER   FIRST    BICUSPID.  119 

2d.  Divide  the  tooth  from  huccal  to  lingual  through  its 
length  with  a  fine  saw,  or  remove  the  distal  half  of  the 
tooth  with  the  file  or  stone.  These  two  dissections  will 
usually  exhibit  the  pulp  chamber  and  root  canals  sufiiciently, 
though  in  the  single-rooted  teeth  with  two  canals  it  is  better 
to  divide  the  root  crosswise  at  the  middle  of  its  lens^th,  or 
at  several  points. 

PULP  CHAMBER  OF  THE  UPPER  FIRST  BICUSPID. 

167.  The  pulp  chamber  and  root  canals  of  this  tooth 
differ  from  those  of  the  incisors  and  cuspids,  by  having  the 
coronal  chamber  distinguished  sharply  from  the  root  canals 
(Fig.  113,  f/,  e).  The  chamber  is  centrally  located  in  the  long 
axis  of  the  crown  of  the  tooth,  the  axial  walls  bein^  about 
equal  in  thickness.  The  center  of  the  pulp  chamber  is  about 
level  with  the  gingival  line,  or  a  little  toward  the  occlusal 
surface.  The  occlusal  walls  are  thicker  than  the  axial,  and 
vary  in  thickness  from  one-third  to  two-thirds  of  the  length 
of  the  crown  of  the  tooth.  The  form  of  the  pulp  corresponds 
closely  with  the  form  of  the  tooth.  A  horn  extends  from 
the  coronal  portion  toward  the  apex  of  each  cusp.  The 
buccal  horn  rises  from  the  extreme  buccal  part  of  the  pulp, 
while  the  lingual  horn  rises  from  the  extreme  lingual  por- 
tion. Sometimes,  especially  in  long  cusj^id  teeth,  they  are 
very  long  and  slender,  extending  far  toward  the  points  of  the 
cusps,  and  in  rare  cases  almost,  or  even  quite  to  the  enamel. 
As  age  advances,  they  become  shorter,  and  in  old  age  have 
almost  disappeared.  In  thick-necked  teeth  with  short  cusps, 
the  horns  of  the  pulp  chamber  are  short,  and  the  occlusal  wall 
is  usually  very  thick. 

The  root  canals  in  upper  first  bicuspids  that  have 
two  roots  pass  from  the  pulp  chamber  through  the  center  of 
each  root  to  its  apex,  and  are  known  as  the  buccal  and  lin- 
gual root  canals  (e).  The  buccal  canal  arises  from  the  ex- 
treme buccal  side  of  the  pulp  chamber,  and  the  lingual  canal 


120  PULP  CHAMBER — UPPER  SECOND  BICUSPID— LOWER  BICUSPIDS. 

from  the  extreme  lingual  side,  and  their  course  is  almost 
parallel  with  the  walls  of  these  two  portions  of  the  pulp 
chamber.  The  floor  of  the  chamber  is  rounded  over  in  an 
arch  from  one  canal  to  the  other.  Each  canal  begins  in  a 
funnel-shaped  opening  leading  into  a  narrow  round  canal, 
which  tapers  gradually  to  the  apical  foramen.  Many  of  the 
upper  first  bicuspids  have  only  one  root ;  but  they  generally 
have  two  root  canals  almost  exactly  similar  to  those  with 
two  roots.  Occasionally,  however,  these  come  together  and 
end  in  one  apical  foramen,  or  there  may  be  a  communication 
between  the  two  canals  in  some  part  of  their  course  (d). 
More  rarely,  the  upper  first  bicuspid  has  one  broad  (from 
buccal  to  lingual)  flat  canal  passing  through  the  whole  length 
of  its  sing-le  root.  Sometimes  this  is  divided  near  the 
apex  (b). 

PULP  CHAMBER  OF  THE  UPPER  SECOND  BICUSPID. 

168.  The  pulp  chamber  of  the  upper  second  bicuspid 
<Fig.  114)  is  similar  to  that  of  the  first  {q.  v.,  Par.  167);  but  the 
horns  of  the  pulp  are  usuall}^  shorter.  In  this  tooth  there  is 
generally  but  a  single  root  canal  (e,/).  This  is  approached 
by  an  opening  that  is  broad  bucco-lingually,  and  tapers  gradu- 
ally toward  the  apex  of  the  root,  ending  in  a  narrow  apical 
foramen.  The  canal  is  often  quite  large,  and  the  demarkation 
of  the  pulp  chamber,  as  distinguished  from  the  root  canal, 
very  indistinct,  or  entirely  absent.  Examples  are  not  infre- 
quent, however,  in  which  there  are  two  root  canals  in  the 
single  root  (d).  They  are  then  similar  to  those  of  the  first 
bicuspid ;  but,  sometimes,  the  two  canals  end  in  a  common 
apical  foramen  (a). 

PULP  CHAMBERS  OF  THE  LOWER  BICUSPIDS. 

169.  The  pulp  chambers  of  the  lower  bicuspids  (Figs. 
115  and  116)  seldom  show  a  marked  distinction  from  the  root 
canals.     There  is,  however,  usually  a  coronal  bulbous  portion 


PULP   CHAMBERS   OP   THE   UPPER   MOLARS.  121 


which  connects  with  the  pulp  canal  proper  by  an  extended 
funnel-shaped  constriction  (a,  b).  In  the  lower  first  bicuspid, 
the  coronal  extremity  ends  in  a  horn,  which  extends  toward 
the  point  of  the  buccal  cusp.  This  horn  may  be  short  and 
obtuse,  or  long  and  pointed.  There  is,  generally,  a  well 
marked  protrusion  toward  the  lingual  cusp,  but  no  extended 
horn.  It  is  rather  an  enlargement  of  the  bulb  in  that  direc- 
tion. In  the  lower  second  bicuspid  this  protrusion  is  more 
considerable,  and  in  some  examples  it  is  elongated  into  a 
slender  point,  especially  in  young  teeth  (Fig.  116,  b).  In  the 
three  cusped  lower  second  bicuspids  (Par.  62,  Fig.  49)  there 
are  two  of  these  on  the  lingual  side,  spreading  toward  the 
mesial  and  distal.  They  are  generally  short,  but  by  their 
protrusion  are  brought  rather  nearer  the  surface  of  the  tooth 
than  other  horns  of  the  pulp  ;  and  are,  therefore,  more  liable 
to  be  opened  into  when  excavating  proximate  cavities. 

170.  The  root  canals  of  the  lower  bicuspids  are  usually 
large  in  the  first  half,  tapering  to  a  fine  canal  in  the  apical 
third,  of  their  length.  The  canal  of  the  lower  first  bicuspid 
is  usually  nearly  round,  and  that  of  the  second  is  considerably 
flattened ;  and  in  both  they  are  usually  straight.  Bifurca- 
tions of  these  canals  are  rare,  but  occur  occasionally.  In  the 
illustrations  (Fig.  115,  6)  one  is  shown  dividing  in  such  a 
way  that  the  division  would  not  be  likely  to  be  detected  by 
a  broach. 

PULP    CHAMBERS    OF   THE   UPPER   MOLARS. 

171.  Dissections. — 1st.  With  a  fine  saw,  separate  the 
crown  from  the  root  level  with  the  gingival  line. 

2d.  Cut  away  the  mesial  surface  of  the  crown  and  the 
mesial  surface  of  the  mesial  and  lingual  roots,  with  the  file 
or  a  corundum  stone,  till  the  canals  in  each  are  fully  exposed. 
As  the  mesial  root  is  generally  curved,  some  care  is  required 
to  fully  expose  the  full  length  of  the  canal  without  cutting 
too  far  in  the  central  portion  of  its  length.  If  the  curved 
surface  is  made  smooth,  good  prints  can  generally  be  made 


122  PULP   CHAMBERS    OF    THE   UPPER   MOLARS. 

by  using  a  piece  of  semi-soft  rubber  under  the  paper,  and, 
while  pressing  it  to  the  paper,  rolling  the  tooth  so  as  to  bring 
all  of  the  length  of  the  curved  surface  in  contact. 

3d.  Cut  away  the  buccal  surface  so  as  to  expose  the 
pulp  chamber  and  canals  of  the  two  buccal  roots,  observing 
the  same  precautions  as  in  the  second  dissection. 

In  the  first  dissection,  both  crown  and  root  should  be 
examined.  First,  clean  the  portion  of  the  chamber  in  the 
crown,  to  studj'  carefully  its  horns  and  its  general  shape  or 
contour  with  relation  to  the  outer  surface  of  the  tooth.  The 
roQt  canals  should  be  cleaned  with  the  broach,  and  their  size 
and  dir'ection  carefully  studied  ;  also,  the  position  of  the 
openings  leading  from  the  pulp  chamber  should  be  studied 
with  regard  to  their  i-elation  to  the  several  points  of  the  sur- 
face of  the  crown.  This  latter  is  especially  important.  Several 
dissections  should  be  made  of  each  of  the  upper  molars. 

4th.  Grind  away  the  root  portion  of  the  first  dissec- 
tion, printing  occasionally  till  the  bifurcation  of  the  roots  is 
reached. 

172.  The  pulp  chamber  of  the  upper  molars  is  very 
distinct  from  the  pulp  canals,  the  latter  often  leaving  the 
former  by  very  small  openings  (Fig.  117).  The  average 
diameter  of  the  pulp  chamber  is  about  equal  to  the  thickness 
of  the  axial  walls  by  which  it  is  surrounded,  sometimes 
more,  sometimes  less.  The  occlusal  wall  is  usually  con- 
siderably thicker.  The  form  of  the  pulp  chamber  is  gener- 
ally similar  to  that  of  the  crown  of  the  tooth  ;  but  the  horns 
in  the  young  tooth  are  often  quite  slender  as  compared  with 
the  cusps,  and  penetrate  far  toward  the  enamel.  The  length 
of  these  diminishes  as  age  advances.  In  teetli  much  flattened 
mesio-distally,  as  often  occurs  in  the  upper  first  molars,  and 
especially  with  the  second,  the  equal  thickness  of  the  axial 
walls  is  usually  maintained  pretty  closely,  so  that  the  flat- 
tening of  the  pulp  chamber  seems  out  of  proportion  to  the 
form  of  the  tooth. 


ay 


Fig.  117. 


D&OOOd 


Fig.  118. 


Fig.  119. 


Fig.  120. 


Fig.  121. 


Fig.  117*  (Par.  172).— Pulp  Chamber  and  Root  Canals  of  the  Upper  First  Molar. 
a,  c,  mesio-distal  sections,  showing  the  pulp  chamher  and  the  canals  in  the  mesial  and 
distal  roots ;  b,  bucco-lingual  section,  sho\ying  the  pulp  chamber  and  the  canals  in  the 
mesial  and  lingual  roots ;  d,  bucco-lingual  section,  showing  the  chamber  and  the  canals 
in  the  distal  and  lingual  roots. 

Figs.  118,*  119*  (Par.  173).— Pulp  Chamber  and  Root  Canals  of  the  Upper  First 
Molars,  cross-sections,  o.  Centrally  through  the  pulp  chamber ;  5,  section  just  at  the 
floor  of  the  pulp  chamber ;  c,  section  a  little  rootwise  from  the  pulp  chamber,  showing 
the  canals  and  the  form  of  the  molar  triangle. 

Fig.  120*  (Par.  177).— Pulp  Chamber  and  Root  Canals  of  the  Upper  Second  Molar. 
a,  Mesio-distal  section,  showing  pulp  chamber  and  the  canals  in  the  mesial  and  distal 
roots ;  6,  bucco-lingual  section,  showing  the  chamber  and  the  canals  in  the  distal  and 
lingual  roots. 

Fig.  121*  (Par.  178).— Pulp  Chamber  and  Root  Canals  in  the  Upper  Third  Molar. 
a,  Bucco-lingual  section,  showing  pulp  chamber  and  the  canals  in  the  mesial  and  lingual 
roots ;  b,  mesio-distal  section  of  a.  single  rooted  tooth,  showing  the  form  of  the  pulp 
chamber  and  the  mesial  and  distal  root  canals. 


*  Illustration,  actual  size. 


PULP   CHAMBERS    OF    THE    UPPER   MOLARS.  125 


173.  The  floor  of  the  pulp  chamber  is  rounded  or 
arched  in  the  center,  and  falls  away  toward  the  mouths  of 
the  canals.  The  latter  are  situated  in  the  position  of  the 
angles  of  a  triangle  {the  molar  triangle)  (Figs.  118  and  119), 
the  mesial  line  of  which  is  the  longest,  the  buccal  the  short- 
est, and  the  distal  the  intermediate  length.  For  the  upper 
first  molar,  this  triangle  is  well  shown  in  the  illustrations 
representing  sections  a  little  rootwise  from  the  floor  of  the 
pulp  chamber  (c).  This  is  best  seen  in  the  specimen  itself; 
and  the  position  and  the  direction  of  the  canals,  with  relation 
to  the  walls  of  the  pulp  chamber  and  the  main  points  of  the 
surface  of  the  crown,  should  be  carefully  studied. 

174.  The  opening  into  the  lingual  root  (Fig.  117,  h)  is 
the  simplest  and  most  direct.  Generally,  it  begins  in  a  fun- 
nel-shaped opening  inclining  to  the  lingual,  which  quickly 
narrows  to  the  dimensions  of  a  moderately  small  canal,  and 
continues  to  taper  to  the  apical  foramen.  It  is  usually 
straight,  or  but  slightly  curved. 

175.  The  opening  into  the  mesial  canal  is  under  the 
mesio-buccal  cusp,  close  against  the  mesio-buccal  angle  of 
the  pulp  chamber.  It  often  happens  that  this  canal  begins 
in  a  groove  in  the  angle  of  the  chamber  (Fig.  119,  h),  mak- 
ing this  the  thinnest  point  in  the  dentinal  walls  surrounding 
it.  In  young  teeth,  the  mouth  of  the  canal  is  of  a  flattened 
funnel-shape,  which  is  quickly  contracted  into  a  very  fine 
canal ;  but  in  the  adult,  it  often  begins  as  a  fine  canal.  Its 
course  at  first  is  to  the  buccal  and  mesial,  and  then  curves  to 
the  distal.  It  is  usually  distinctly  flattened,  and  often  has 
a  thin  edge  to  the  lingual.  It  is  often  a  very  difiicult  canal 
to  clean  with  a  broach.  To  find  this  canal  the  point  of  the 
broach  should  be  directed  into  the  mesio-buccal  angle  of 
the  pulp  chamber ;  and,  while  held  against  the  wall  within 
this  angle,  it  is  slid  toward  the  root.  It  will  rarely  fail  to 
glide  into  the  canal. 

176.  The  distal  canal  usually  begins  abruptly  as  a  fine 


126  PULP    CHAMBERS   OF    THE    UPPER   MOLARS. 


opening  (Fig.  117,  a,  c),  situated  at  the  disto-buccal  angle  of 
the  floor  of  the  pulp  chamber  (Figs.  118  and  119) ;  so  that  a 
broach  pressed  into  that  angle  will  easily  glide  into  it.  But 
in  some  instances,  especially  in  the  upper  second  molars,  the 
opening  is  in  the  floor  of  the  pulp  chamber  at  a  little  distance 
from  the  immediate  angle  toward  the  center  of  the  floor,  and 
then,  in  positions  which  limit  the  use  of  the  eye,  it  is  often 
difiicult  to  find.  In  teeth  much  flattened  at  the  neck,  the 
opening  of  this  canal  may  begin  very  close  to  the  mouth  of 
the  mesial  canal  (Fig.  120,«),  or  close  against  the  distal  wall 
of  the  chamber,  half-way  from  the  buccal  to  the  lingual 
wall,  or,  anywhere  between  this  point  and  the  disto-buccal 
angle.  The  first  direction  of  the  canal  will  vary  according 
to  its  position.  If  it  is  found  in  a  fairly  v:ell-defined  disto- 
buccal  angle  of  the  chamber,  its  direction  will  be  a  little 
inclined  to  the  distal,  and  the  broach  will  penetrate  it  easily; 
if  in  the  floor  of  the  chamber,  it  will  sometimes  be  straight, 
as  in  the  former  case ;  but  more  generally  the  first  direction 
will  be  to  the  distal  and  buccal,  with  considerable  curve 
afterward.  If  found  close  to  the  mesial  canal,  its  coarse  is 
usually  first  sharply  to  the  distal,  when  it  curves  rather 
abruptly  toward  the  apex  of  root.  If  found  along  a  smooth 
or  curved  distal  wall,  the  course  will  generally  be  to  the 
distal  and  buccal,  with  but  little  curve.  This  canal  is  usually 
very  fine  from  its  beginning,  and  almost  or  quite  round. 

177.  While  the  canals  are  similar  in  all  of  the  upper 
molars,  there  are  difterences  in  the  form  of  the  floor  of  the 
pulp  chamber  that  may  be  briefly  generalized.  The  pulp 
chamber  of  the  upper  second  molar  (Fig.  120)  is  usually  much 
more  flattened  from  mesial  to  distal  than  in  the  first  molar. 
This  changes  the  relation  of  the  mouths  of  the  canals  some- 
what, rendering  the  distal  angle  of  the  triangle  formed  by 
them  more  obtuse,  and  brings  the  mouth  of  the  distal  canal 
nearer  the  mesial  line  of  the  triangle,  so  that  it  seems  to  be 
found  alono;  the  distal  wall  of  the  narrowed  chamber.     In 


§0  9$ 


Fig.  122. 


By 


9 


Fig.  12-' 


V^^ 


Fig.  125. 

Fig.  122*  (Par.  180).— Pulp  Chamber  and  Root  Canals  of  the  Lower  First  Molar, 
a,  b,  Mesio-ciistal  sections,  showing  the  form  of  the  pulp  chamber  and  root  canals ;  c. 
bucco-lingual  section,  showing  the  canals  in  the  mesial  root. 

Fig.  123*  (Par.  180).— Cross-sections  Through  the  Crown  and  Root  of  the  Lower 
Fit  ST  Molar,  showing  the  pulp  chamber  and  the  root  canals,  d,  (i,  Sections  through  the 
pulp  chamber ;  e,  h,  sections  a  little  root  wise  from  the  pulp  chamber  ;  /,  /,  sections  near 
apex  of  root. 

Fig.  124*  (Par.  180).— Polp  Chamber  and  Root  Canals  of  the  Lower  Second  Molar. 
a,  c,  Mesio-distal  sections,  showing  the  form  of  the  pulp  chamb'er  and  root  canals;  h, 
bucco-lingual  section  of  the  distal  root  and  crown  ;  (/,  bucco-lingual  section  through  the 
mesial  root  and  crown,  showing  two  canals  with  communication  in  the  apical  third  of 
the  root.    This  communication  is  not  very  common. 

Fig.  125*  (Par.  182).— Pulp.Chamber  anitRoot  Canals  of  the  Lower  Third  Molar. 
a,  c,  In  double-rooted  teeth  ;  h,  single-rooted  teeth. 


*  Illustration,  actual  size. 


PULP    CHAMBERS   OF   THE    LOWER   MOLARS.  129 

others,  it  is  found  in  the  extreme  buccal  portion  crowded 
close  against  the  mouth  of  the  mesial  canal. 

178.  The  position  of  the  openings  of  the  canals  in  the 
upper  third  molar  (Fig.  21)  is  usually  much  the  same  as  in 
the  first  and  second,  varying  so  as  to  resemble  either.  Occa- 
sionally there  is  more  than  the  usual  number ;  and  others 
with  only  one  or  two.  When  there  is  but  one,  it  is  com- 
monly quite  large.  Four,  five,  or  even  seven,  or  eight,  are 
sometimes  found. 

PULP    CHAMBERS    OF    THE    LOWER   MOLARS. 

179.  Dissections. — 1st.  Saw  the  tooth  through  the  gin- 
gival line  dividing  the  crown  from  the  root.  This  cut  will 
pass  through  the  body  of  the  pulp  chamber  and  give  a  good 
view  of  the  roof,  and  floor,  and  a  good  idea  of  the  general 
form.  The  root  canals  should  be  cleaned  and  examined  with 
the  broach. 

2d.  Saw  the  tooth  through  from  end  to  end  centrally 
from  mesial  to  distal,  or  grind  or  file  away  the  buccal  side 
till  the  pulp  chamber  and  the  root  canals  are  exposed.  As 
there  are  usually  two  canals  in  the  mesial  root,  an  exact 
central  cut  from  mesial  to  distal  will  generally  fail  to  expose 
the  canals,  and  the  cut  will  be  better  made  at  a  slight 
angle,  so  as  to  expose  either  the  buccal  or  lingual'canal  of  the 
mesial  root. 

3d.  Grind,  or  file,  away  the  mesial  surface  of  the  crown 
and  root  till  the  pulp  chamber  and  the  whole  length  of  the 
canals  in  the  mesial  root  are  exposed.  As  this  root  is  usually 
curved,  the  cutting  must  be  done  with  care,  and  the  curve 
followed. 

4th.  Cross  sections  of  the  roots  should  be  made  at 
intervals.  An  excellent  study  is  to  begin  grinding  at  the 
apex  of  the  roots,  printing  occasionally,  and  continuing  the 
grinding  until  the  pulp  chamber  is  reached.  This  will  display 
cross-sections,  at  intervals,  of  the  entire  root  canals.    Enough 

K 


130  PULP   CHAMBERS   OF   THE   LOWER   MOLARS. 

of  these  dissections  should  be  made,  of  each  of  the  lower 
molars,  to  make  the  student  familiar  with  each  class. 

180.  The  pulp  chamber  of  the  lower  molars  (Figs.  122 
123,  124)  has  the  same  general  form  as  the  surface  of  the 
'Crown,  but  is  generally  rather  more  angular.  The  wall  of 
the  chamber  toward  the  occlusal  surface  is  convex  toward 
the  pulp  ;  the  horns  extend  from  the  extreme  angles  toward 
the  apex  of  each  cusp.  The  floor,  through  the  central  por- 
tion is  arched  or  convexed,  mesio-distallj,  and  concave 
bucco-lingually.  The  mesial  wall  of  the  cavity  is  flat, 
and  longer  than  the  distal.  The  mesio-buccal  and  mesio- 
lingual  angles  are  sharp  and  projecting,  Mdiile  the  distal 
angles  are  rounded  (Fig.  123,  cZ,  g).  The  size  of  the  chamber, 
varies  much.  In  youth,  its  diameter  is  often  as  much  as  two- 
fifths  of  the  crown,  and  seldom  less  than  one-third.  This 
diminishes  as  age  advances,  and  in  old  age  it  is  often  verj 
small,  or  especially  where  there  has  been  considerable  abra- 
sion of  the  teeth,  the  pulp  chamber  may  be  almost  obliterated. 

181.  The  root  canals  of  the  lower  molars  proceed  from 
the  mesial  and  distal  portions  of  the  pulp  chamber  (Fig.  122, 
«,  h).  The  mesial  canal,  at  its  mouth,  is  usually  about  as 
broad  from  buccal  to  lingual  as  the  whole  breadth  of  the  . 
chamber,  including  its  angular  projections.  Either  at,  or  a 
little  rootwise  from  the  floor  of  the  pulp  chamber,  it  is  usu- 
ally divided  into  two  very  small  canals  which  diverge  at 
first,  and  approach  each  other  afterward,  but  usually  remain 
distinct,  each  ending  in  its  own  apical  foramen  (Fig.  122,  c). 
Occasionally,  however,  they  are  united  in  the  apical  third  of 
the  root,  and  end  in  a  common  apical  foramen.  Again,  there 
ma}'  be  a  communication  between  them  intheapijal  portion 
of  the  root,  each  canal  remaining  otherwise  C0ixi|.»icjte  in  itself. 
A  few  have  one  broad  flattened  canal  (Fig.  123,  <:/,  e,  /). 
These  canals  are  usually  minute,  and  verj'  .difiicult  to  thor- 
oughly clean  with  the  broach,  though  the  mesio-buccal  canal 
is  usualh'  easily  found,  if  the  pulp  chamber  is  thoroughly 


VARIATIONS    OF    THE    FORM    OF   PULP    CHAMBERS.  131 

opened.  Bj  placing  the  point  of  the  broach  in  the  mesio- 
buccal  angle  of  the  chamber  and  pushing  it  gently  on,  it 
will  generally  glide  into  the  canal.  The  first  direction 
inclines  to  the  mesial  and  buccal,  after  which  it  curves  to 
the  distal  and  lingual  (Fig.  122,  e).  Generally  these  curves 
are  easy,  without  short  bends.  The  broach  easily  glides  into 
the  mesio-lingual  canal  by  p)lacing  the  point  in  the  mesio- 
lingual  angle  of  the  pulp  chamber  and  sliding  it  toward  the 
root.  The  first  inclination  is  to  the  mesial,  but  occasionally 
to  the  lingual,  after  which  it  curves  to  the  distal  and  buccal. 

182.  The  distal  canal  is  approached  by  a  funnel-shaped 
opening,  of  which  the  central  part  of  the  distal  wall  of  the 
pulp  chamber  becomes  a  portion.  Its  direction  is  a  little  to 
the  distal,  and  is  generally  very  nearly  straight  to  the  apex. 
At  first,  it  is  flattened,  with  the  long  diameter  from  buccal 
to  lingual,  and  progressively  becomes  rounded,  and  tapers 
regularly  to  the  apical  foramen.  It  is  generally  much  larger 
than  the  canals  of  the  mesial  root,  and  is  easily  cleaned  with 
the  broach.  If  the  mouth  is  wide  open,  and  the  handle  of 
the  broaqh  brought  against  the  upper  central  incisors  with 
the  point  directed  against  the  posterior  wall  of  the  pulp 
chamber,  it  will  easily  glide  into  the  canal,  and  pass  to  the 
apical  foramen.  This  particular  position  for  easily  entering 
the  distal  canal  is  important,  for  all  the  lower  molars.  Occa- 
sionally, the  lower  third  molar  has  but  one  root  canal  (Fig. 
125, 6),  which  is  then  generally  very  large.  More  rarely,  onl}^ 
a  single  canal  will  be  found  in  the  lower  second  molar,  but 
generally  the  canals  of  the  second  and  third  lower  molars  are 
similar  to  those  of  the  first.  The  pulp  chambers  are  usually 
smaller,  and  oftener  irregular  in  outline.  The  lower  third 
molar  has,  occasionally,  a  very  large  pulp  chamber. 

VARIATIONS    OF    THE    FORM    OF    PULP    CHAMBERS. 

183.  Many  variations  of  form  occur  in  the  pulp  cham- 
bers and  root  canals.     The  roots  of  the  teeth  may  be  abnor- 


132  PULP   CHAMBERS   OF    THE    DECIDUOUS    TEETH. 


mally  crooked;  and  then  the  canals  will  be  abnormally 
crooked.  In  many  instances,  the  pulp  chamber  will  have  in 
it  secondary  formations,  called  nodules,  which  may  be  ad- 
herent to  the  walls,  or  block  the  mouths  of  the  canals  and 
prevent  a  broach  gliding  into  them.  These  also  occur, 
occasionally,  within  the  canals,  partially  blocking  the  way 
of  the  broach.  Sometimes  the  pulp  chamber  will  be  filled 
with  nodular  deposits  so  completely  that  there  seems  to  be 
no  room  for  the  tissues  of  the  pulp.  These  deposits  will 
have  to  be  removed  before  the  root  canals  can  be  reached 
and  entered,  after  which  the  canals  will  generally  be  found 
open.  These  deposits  occur  within  the  pulp  chambers  of  any 
of  the  teeth ;  but  they  cause  annoyance  more  frequently  in 
the  molars. 

184.  Occasionally  lateral  openings  occur  from  the  root 
canals  to  the  surface  of  the  root.  I  have  seen  more  of  these 
from  the  canals  of  the  lower  molars  than  from  those  of  any 
other  teeth.  Generally,  they  follow  the  course  of  the  dental 
tubules,  and  open  on  the  side  of  the  root.  They  may  diverge 
to  one  side  and  curve  toward  the  apex  of  the  root.  These 
cannot  often  be  detected,  except  in  dissections  of  the  root, 
and  occur  so  rarely  they  may  be  ignored  in  practice. 

185.  Sometimes  the  horns  of  the  pulp  approach  abnor- 
mally near  the  points  of  the  cusps  of  some  of  the  teeth,  as  in 
the  upper  first  bicuspids,  and  in  the  mesio-buccal  cusp  of  the 
upper  first  molar.  Then  the  pulp  is  more  liable  to  exposure 
in  excavating  carious  cavities. 

PULP    CHAMBERS    OF    THE    DECIDUOUS    TEETH. 

186.  The  pulp  chambers  of  the  deciduous  teeth  are- 
pruportionately  larger,  and  the  thickness  of  their  walls  less, 
than  those  of  the  corresponding  permanent  teeth.  The  pulps 
are,  in  consequence,  exposed  with  much  less  penetration  of 
tooth  substance,  and,  therefore,  more  liable  to  exposure  from 
caries,  or  in  the  use  of  cutting  instruments.     The  root  canals 


Fi.ar.l26. 


Fig.  126  (Par.  187).— The  Elliptical  Form  of  the  Arch.  The  crowns  of  the  teeth  of 
both  upper  and  lower  jaws,  drawn  from  the  casts  of  a  very  regularly-formed  arch,  and 
the  line  of  a  true  ellipse  (in  dots)  placed  over  them,  showing  the  comparative  size  of  the 
upper  and  lower  arch,  and  the  deviations  from  perfect  regularity. 


ARRANGEMENT  OF  THE  TEETH.  135 


are  generally  larger  than  in  the  permanent  teeth  of  the  same 
denomination,  but  are  of  the  same  general  form.  Also,  the 
same  rules  for  finding  the  root  canals  in  the  permanent  molars 
apply  to  the  deciduous.         * 

ARRANGEMENT  OF  THE  TEETH. 

187.  The  upper  teeth  are  arranged  in  the  form  of  a 
semi-ellipse,  the  long  axis  passing  between  the  central  inci- 
sors (Figs.  126  and  127).  In  this  curve,  the  cuspids  stand  a 
little  prominent,  giving  a  fullness  to  the  corners  of  the  mouth- 
In  different  persons  there  is  much  variation  of  the  form  of 
the  arch  within  the  limits  of  the  normal.  Occasionally  the 
bicuspids  and  molars  form  a  straight  line,  instead  of  a  curve, 
and  frequently  the  third  molars  are  a  little  outside  the  line 
of  the  ellipse.  In  the  examination  of  casts  of  the  most  per- 
fect dentures  it  is  found  that  the  two  sides  do  not  perfectly 
correspond,  and  that  certain  teeth  deviate  slightly  from  the 
perfect  line.  The  incisors  are  arranged  with  their  cutting 
edges  forming  a  continuous  curved  line  from  cuspid  to  cus- 
pid, and  this  line  is  continued  over  the  cusps  of  the  cuspids, 
and  the  buccal  cusps  of  the  bicuspids  and  molars  to  the  dis- 
tal surface  of  the  third  molars.  From  the  first  bicuspid  to 
the  third  molar  the  lingual  cusps  of  these  teeth  form  a  sec- 
ond line  of  elevations.  Between  these  two,  the  lingual  and 
buccal  cusps,  there  is  a  continuous  but  irregular  valley,  or 
sulcus. 

188.  The  lower  teeth  are  arranged  similarly  (Fig. 
185)  but  on  a  slightly  smaller  curve,  so  that  the  line  of  the 
ellipse,  which  falls  on  the  buccal  cusps  of  the  upper  bicuspids 
and  molars,  will  fall  upon  the  buccal  surfaces  near  the  gum 
on  the  lower  teeth  (Fig.  120).  Therefore  in  occlusion  the 
upper  teeth  project  a  little  to  the  labial  and  buccal  of  the 
lower  at  all  points  of  the  arch  (Fig.  131).  The  incisors  and 
cuspids  occlude  so  that  the  cutting  edges  of  the  lower  in- 
cisors and  cusps  of  the  cuspids  make  contact  with  the  lingual 


136  ARRANGEMENT  OF  THE  TEETH. 

surfaces  of  the  similar  teeth  of  the  upper  jaw  near  their  cut- 
ting edges  (Fig.  128).  In  this,  however,  there  is  much 
variety  within  the  limits  of  a  normal  occlusion.  Sometimes 
the  lower  incisors  strike  the  Ihigual  surfaces  of  the  upper 
near  the  linguo-gingival  ridge,  and  may  strike  at  any  point 
between  that  and  the  cutting  edges.  In  abnormal  occlusions 
the  lower  incisors  may  miss  the  upper,  striking  the  gums 
posterior  to  them,  or  they  may  occlude  anterior  to  the  upper 
incisors.  The  broad  cusped  occlusal  surfaces  of  the  bicus- 
pids and  molars  of  the  opposing  dentures  rest  on  each  other 
in  such  a  way  that  the  lingual  cusps  of  the  upper  teeth  fit 
Avith  more  or  less  accuracy  into  the  general  sulcus  formed 
between  the  buccal  and  lingual  cusps  of  the  lower  teeth. 
The  buccal  row  of  cusps  of  the  lower  teeth,  in  a  similar  way, 
are  fitted  into  the  sulcus  formed  between  the  buccal  and  lin- 
gual cusps  of  the  upper  teeth  (Figs.  129  and  130).  This 
arrangement  is  such  that  when  the  teeth  are  in  occlusion,  it 
leaves  the  buccal  inclines  of  the  buccal  cusps  of  the  upper 
teeth  outside  the  buccal  surface  of  the  lower  teeth  (a).  And, 
also,  leaves  a  ledge  formed  by  the  abrupt  lingual  inclines  of 
the  lingual  cusps  of  the  lower  teeth  along  the  lingual  line  of 
the  occlusion  (6).  This  brings  the  occlusal  surfaces  of  the 
teeth  in  the  best  form  of  apposition  for  the  purposes  of  mas- 
tication. The  forms  presented  to  the  cheek  and  to  the  tongue 
hold  these  soft  tissues  a  little  apart  from  the  actual  contact 
points  of  the  occlusion,  and  thus  prevent  them  from  being 
caught  and  pinched,  or  crushed,  between  the  teeth  in  the  act 
of  mastication.  In  youth,  while  the  permanent  teeth  are 
taking  their  places,  and  before  the  cusps  are  properly  fitted 
to  the  sulci,  we  often  find  the  cheeks  or  tongue  wounded  by 
being  caught  between  falsely  occluded  points.  With  the  after 
movements  of  the  teeth  by  which  they  are  more  perfectly 
arranged,  this  difiiculty  disappears. 

189.     The   line   from   before  backward   on  which  the 
occlusion  occurs  is  not  quite  a  plane ;  in  the  lower  jaw  it 


Fig.  127. 


Fig.  128. 


Fig.  130. 


Fig.  127*  (Par.  IS").— Arrangement  of  the  Teeth  in  the  Arch.    The  arch  of  the 
upper  jaw. 

(Par.  210). — The  Teeth  and  the  Gums  and  the  Rug^  of  the  Roof  of  the  Mouth. 
Fig.  128  (Par.  188).— Labio-Lingual  Position  of  the  Incisors  in  Occlusion. 
Fig.  129  (Par.  188).— Bucco-Lingual  Position  of  the  Bicuspids  in  Occlusion. 
Fig.  130  (Par.  188).— Bucco-Lingual  Position  of  the  Molars  in  Occlusion. 


*  Illustration,  actual  size. 


ARRANGEMENT  OF  THE  TEETH.  139 

presents  a  slight  curve,  or  concavity,  and  in  the  upper  jaw  a 
convexity  (Fig.  131,  c  to  d).  This  concavity  of  the  line  of 
the  occlusal  surfaces  of  the  lower  teeth  is  a  little  greater  than 
the  convexity  of  the  upper,  so  that  the  cutting  edges  of  the 
lower  incisors  pass  a  little  beyond,  and  to  the  lingual  of  the 
cutting  edges  of  the  upper  incisors. 

190.  In  the  occlusion,  the  relative  mesio-distal  position 
of  the  particular  teeth  of  the  upper  jaw  to  the  lower  is  im- 
portant (Fig.  131).  At  their  cutting  edges,  the  upper  central 
incisors  are  about  one-third  wider  mesio-distally  than  the 
lower  centrals.  The  upper  central,  therefore,  occludes  with 
the  lower  central,  and  also  with  from  one-third  to  one-half 
of  the  lower  lateral  incisor.  The  upper  lateral  occludes 
with  the  remaining  portion  of  the  lower  lateral,  and  the  me- 
sial portion  of  the  lower  cuspid.  The  upper  cuspid  is  usually 
^rather  broader  mesio-distally  than  the  lower,  and  in  occlu- 
sion covers  its  distal  two-thirds  and  about  half  of  the  lower 
first  bicuspid,  so  that  its  lingual,  or  triangular  ridge,  is  be- 
tween the  cusp  of  the  lower  cuspid  and  the  buccal  cusp  of 
the  lower  first  bicuspid,  the  point  of  its  cusp  overlapping 
the  lower  teeth.  The  buccal  cusp  of  the  lower  first  bicuspid 
occludes  in  the  space  between  the  upper  cuspid  and  upper 
first  bicuspid.  This  order  is  now  maintained  between  the 
bicuspids.  The  buccal  cusp  of  the  upper  first  bicuspid  over- 
laps (to  the  buccal)  the  space  between  the  two  lower  bicus- 
pids, and  its  lingual  cusp  occludes  in  the  sulcus  between 
them,  while  the  buccal  cusp  of  the  lower  second  bicuspid 
occludes  in  the  sulcus  between  the  two  upper  bicuspids.  The 
cusps  of  the  upper  second  bicuspid  occlude  between  the 
lower  second  bicuspid  and  lower  first  molar.  The  broad  sur- 
faces of  the  molars  come  together,  so  that  the  mesial  two- 
thirds  of  the  upper  first  niolar  covers  the  distal  two-thirds 
of  the  lower  first  molar ;  and  the  distal  third  of  the  upper 
first  molar  covers  the  mesial  third  ot  the  lower  second  molar. 
This  brings  the  oblique  ridge'of  the  upper  molar  between 


140  ARRANGEMENT  OF  THE  TEETH. 

these  two  lower  teeth.  This  order  is  continued  between  the 
remaining  molars,  but  less  perfectly  as  the  teeth  are  more 
irregularly  formed.  The  upper  third  molar  is  usually  smaller 
than  the  lower  third  molar,  yet  it  generally  extends  over  its 
distal  surface. 

191.  The  inclination  of  the  teeth  is  the  deviation  of 
their  long  axes  from  the  perpendicular  line.  The  direction 
of  the  inclination  is  expressed  b}^  some  accompanying  word. 
The  upper  incisors  and  cuspids  are  so  arranged  that  their 
crowns  are  inclined  more  or  less  forward,  or  toward  the  lip, 
and  slightly  toward  the  median  line.  The  mesial  inclina- 
tion is  continued  in  the  bicuspids  and  molars,  diminishing 
from  before  backward,  and  is  usually  lost  at  the  second  or 
third  molar.  As  a  rule,  the  bicuspids  and  molars  of  the 
upper  jaw  are  also  slightly  inclined  toward  the  cheek,  but 
in  many  dentures  this  inclination  is  slight,  or  wanting  in 
the  bicuspids  and  first  molars  to  reappear  in  the  second 
and  third  molars,  though  it  may  be  absent  even  in  these 
without  necessary  malformation. 

192.  The  lower  incisors  and  cuspids  are  also  inelined 
with  their  crowns  toward  the  lip,  but  in  less  degree  than 
the  upper.  And  even  the  perpendicular  position  of  these  is 
not  inconsistent  with  a  normal  arrangement.  They  have, 
however,  a  mesial  inclination,  but  usually  much  less  than 
the  corresponding  upper  teeth.  The  lower  bicuspids,  with- 
in the  limits  of  the  normal  arrangement,  vary  considerably 
in  their  inclinations.  Sometimes  they  have  a  strong  mesial 
inclination,  and  at  other  times  they  are  nearly  or  quite  per- 
pendicular. In  many  dentures,  they  also  have  a  lingual 
inclination,  but  may  be  perpendicular  or  even  have  a  slight 
buccal  inclination.  The  lower  molars  usually  have  a  slight 
mesial  and  lingual  inclination  (Fig.  135).  In  many  exam- 
ples, however,  the  mesial  inclination  is  wanting,  especially 
in  the  second  and  third  molars. 

193.  All  the  teeth  are  a  little  broader  mesio-distally  at 


.oL 


^^si^^^^^M^P 


Fig.  131. — Actual  size. 


Fig.  131  (Par.  188).— Arrangement  of  the  Teeth.  Labial  aii<^  buccal  aspect  of 
the  upper  and  lower  teeth  as  arranged  in  the  arch. 

(Par.  197).— The  Alveolar  Process  of  the  Upper  and  Lower  Jaws,  with  the 
Teeth  in  Position. 


ARRANGEMENT  OF  THE  TEETH.  143 

or  near  the  occlusal  surfaces  than  at  their  necks.  Therefore, 
when  arranged  in  the  arch  with  their  proximate  surfaces  in 
contact,  there  is  a  considerable  space  between  their  necks 
(Fig.  131).  These  are  known  as  the  inter-proximate,  or  V- 
shaped,  spaces.  The  sharp  angle  or  apex  of  the  V-form  is 
toward  the  occlusal  surface,  or  at  the  contact  point  of  the 
proximation,  and  the  open  end  or  base  is  at  the  crest  of  the 
alveolar  process  (Figs.  134, 135, 136).  In  normal  conditions, 
this  space  is  filled  by  the  soft  tissues,  or  gunns  (141).  The 
average  arch  measures  about  127  millimeters  (5  inches)  from 
the  distal  surface  of  the  right  third  molar  to  the  distal  sur- 
face of  the  left  third  molar,  following  the  curve  of  the  arch, 
on  the  line  of  the  contact  points  of  the  teeth.  This  repre- 
sents the  average  mesio-distal  measurement  of  the  crowns  of 
the  teeth  of  the  upper  jaw  taken  collectively.  The  average 
measurement  of  the  teeth  at  their  necks  is  about  89  millime- 
ters (3.5  inches).  The  remaining  38  millimeters  (1.5  inches) 
represent  the  average  sum  of  the  inter-proximate  spaces 
taken  collectively. 

194.  On  account  of  differences  in  the  conformation  of 
the  crowns  and  the  inclination  of  the  teeth,  the  inter-proxi- 
mate spaces  vary  much  in  width  in  difterent  dentures.  They 
are  much  wdder  between  bell-crowned  teeth  than  between 
thick-necked  teeth  ;  but  some  inter-proximate  space  exists  in 
every  normal  denture.  When  the  crowns  of  the  incisors  and 
cuspids  are  much  inclined  toward  the  lip,  the  necks  of  the 
teeth  form  a  smaller  circle  than  the  line  of  the  contact  points 
of  the  proximation,  and  in  this  way  the  inter-proximate 
spaces  may  be  considerably  narrowed.  Generally,  the  inter- 
proximate  space  is  wide  between  the  necks  of  the  central  in- 
cisors. The  suture  joining  the  maxillary  bones  passes  be- 
tween the  roots  of  these  teeth,  and  they  are  somewhat  farther 
apart  than  the  roots  of  the  central  and  lateral  incisors,  or 
those  of  the  lateral  incisor  and  the  cuspid.  Therefore,  in 
these  latter,  the  inter-proximate  spaces  are  of  less  width  (Fig. 


144  ARRANGEMENT  OP  THE  TEETH. 

134).  Between  the  bicuspids  the  inter- proximate  spaces  are 
wider  at  the  necks  of  the  teeth  than  between  the  anterior 
teeth,  on  account  of  the  greater  breadth  of  the  crowns  as 
compared  with  the  roots  (Fig,  135,  b).  The  widest  inter- 
proximate  spaces  are  usually  between  the  necks  of  the  molars 
(Figs.  135  and  136,  c). 

195.  The  points  of  proximate  contact  in  the  best  formed 
arches  are  near  the  occlusal  surfaces  of  the  teeth.  In  im- 
perfectly developed  teeth,  in  which  the  crowns  are  much 
rounded  toward  the  occlusal  surfaces,  the  contact  points  are 
more  toward  the  gingival.  In  the  incisors  and  cuspids  they 
are  in  direct  line  with  the  cutting  edges  (Fig.  132,  a).  In  the 
bicuspids  the  contact  is  near  the  mesio-  and  disto-bucco-occlu- 
sal  angles  and  nearly  in  line  with  buccal  cusps  (Fig.  132,  b). 
The  mesial  and  distal  flattened  surfaces  of  these  teeth  con- 
verge to  the  lingual  to  such  an  extent  that,  though  they  are 
arranged  in  arch  form,  the  contact  points  remain  close  to  the 
buccnl  point  angles.  In  many  excellent  dentures  there  is  a 
decided  inter-proximate  space  opening  to  the  lingual,  but  in 
thick-necked  teeth  and  those  of  a  more  rounded  contour,  the 
contact  points  are  often  more  toward  the  lingual,  and  there 
is  no  appreciable  lingual  inter-proximate  space.  In  the  mo- 
lars the  contact  points,  as  a  rule,  are  removed  rather  more  to 
the  lingual,  but  still  in  the  best  formed  dentures  they  will  be 
found  nearly  in  line  with  the  buccal  cusps  (Fig.  132,  c).  Be- 
tween the  upper  first  and  second  molars,  the  contact  point  is 
often  extended  toward  the  lingual  by  the  prominent  disto- 
lingual  cusp  of  the  first  molar ;  and,  even  when  otherwise, 
the  general  rounding  of  the  distal  surfaces  of  the  upper  molars 
often  brings  the  contact  point  near  the  middle  line  of  the 
teeth.  In  lower  first  molars  the  large  distal  cusp  brings  tbe 
contact  point  with  the  second  molar  close  to  the  buccal  side, 
with  a  considerable  lingual  inter-proximate  space  (Fig.  133,  c). 
If  the  distal  cusp  is  small  the  contact  point  is  usually  extended 
toward  the  lingual,  often  as  far  as  half  the  bucco-lingual 


Fig.  132. 


(Ji 


Fig.  133. 


d    c    (j 

Fig.  134. 


Fig.  135. 


Fig.  136. 


Fig.  132  (Pars.  194, 195).— The  Form  of  the  Interproximate  Contact  from  Buccal 
TO  Lingual  of  the  Upper  Teeth.  The  occlusal  surfaces  of  the  teeth  are  ground  away 
until  the  contact  i)oints  are  reached,  and  then  the  outlines  are  accurately  drawn  in 
silhouette,    o.  Incisors ;  b,  bicuspids ;  c,  molars. 

Fig.  133  (Pars.  194, 195).— The  Form,  Bucco-lingually,  of  the  Interproximate  Con- 
tact OF  the  Lower  Molars  and  Bicuspids.  The  occlusal  surfaces  of  the  teeth  were 
ground  away  until  the  contact  points  were  reached  and  the  outlines  accurately  drawn 
in  silhouette,  a.  Contact  of  the  bicuspids  ;  5,  contact  of  the  second  bicuspid  and  first 
molar ;  c,  contact  of  the  first  and  second  molars ;  d,  contact  of  the  second  and  third 
molars. 

Fig.  134  (Pars.  194, 195). — The  Form,  Occluso-gingivally,  of  the  Interproximate-. 
Contact  and  of  the  Interproximate  Spaces  Between  the  Upper  Incisors,  a.  Alveolar- 
process. 

Fig.  135  (Pars.  194, 195).— The  Form,  Occluso-gingivally,  of  the  Interproxim.^te 
Contact  and  OF  the  Interproximate  Spaces  Between  the  Bicuspids  and  Molars  of  the. 
Upper  Jaw.    a,  Alveolar  process  ;  6,  bicuspids  ;  c,  molars. 

Fig.  136  (Pars.  194, 195).— The  Form,  Occluso-gingivally,  of  the  Interproximate- 
Contact  and  of  the  Interpkoximate  Spaces  Between  the  Lower  Bicuspids  and- 
Molars,    a,  Alveolar  process ;  b,  bicuspids ;  c,  molars. 


AKRANGEMENT  OF  THE  TEETH.  147 

breadth  of  the  teeth.  Between  the  second  and  third  molars 
the  contact  point  is  most  frequently  near  the  central  line  of 
the  teeth  (Fig.  133,  d).  In  the  best  formed  dentures  the 
form  of  the  proximate  contact  is  such  as  to  prevent  food 
from  being  crowded  between  the  teeth  in  mastication  ;  and, 
therefore,  such  as  to  keep  these  spaces  clean  and  the  inter- 
proximate  gingivae  in  health.  But  many  faulty  forms  are 
met  with  which  allow  food  to  leak  through  into  the  inter- 
proximate  space  and  crowd  the  gum  away,  forming  a  pocket 
for  the  lodgment  of  debris,  giving  opportunity  for  decom- 
position, and  resulting  in  caries  of  the  proximate  surfaces,  or 
disease  of  the  gum  and  peridental  membrane.  A  close  study 
of  the  forms  of  proximate  contact  in  the  best  formed  dentures 
demonstrate  that  the  immediate  contact  point  is  on  rounded 
prominences  of  the  proximate  surfaces.  The  rounding  of  the 
surfaces  bucco-lingually  is  well  shown  in  Figs.  132,  133,  which 
were  made  by  removing  the  occlusal  surfaces  of  the  teeth  by 
grinding  until  the  contact  points  were  reached,  and  then 
accurately  drawing  the  outlines  to  show  the  form  of  the  con- 
tact points.  In  Figs.  134,  135  and  136,  the  outlines  of  the 
teeth  are  carefully  drawn,  so  as  to  illustrate  the  form  of  the 
contact  occluso-gingivally,  from  which  it  will  be  seen  that 
they  are  sharply  rounded  in  this  direction  also. ,  Therefore 
the  proximate  contact  of  the  teeth  is  such  as  would  be  made 
by  the  contact  of  two  marbles,  or  at  a  single  small  point. 
These  points  of  proximate  contact  also  slide  slightly  upon 
each  other  in  the  act  of  chewing  food,  the  peridental  mem- 
branes allowing  the  teeth  a  slight  motion,  so  that  any  sub- 
stance forced  between  them  easily  glides  out  in  one  way  or 
the  other.  Furthermore,  the  form  of  the  inter-proximate 
gum  tissue,  the  gum  septum,  is  that  of  an  arch  with  its  con- 
vex side  toward  the  point  of  contact  or  occlusal  surfaces  of 
the  teeth.  Therefore  food  material  forced  past  the  rounded 
point  of  contact,  and  lying  loosely  in  the  inter-proximate 
space,  and  upon  this  rounded  and  tolerably  firm  gum  septum 


148  THE   ALVEOLAR   PROCESS   AND   ALVEOLI. 

is  caught  and  carried  away  by  the  gliding  motion  of  food 
over  the  axial  surfaces  of  the  teeth  and  over  the  gum  tissue 
in  the  act  of  chewing.  In  this  way  the  proximate  surfaces 
of  normally  well-formed  teeth  are  kept  free  from  lodgments  as 
long  as  the  gum  septum  retains  its  normal  form  and  firmness. 
In  many  individuals  of  middle,  or  advanced  age,  the  points 
of  proximate  contact  become  much  worn  and  flattened  by 
rubbing  on  each  other  during  mastication.  From  this  cause 
they  often  become  so  broad  as  to  hold  food  material  firmly 
between  them,  which  is  gradually  forced  against  the  gum 
septum,  causing  its  absorption,  and  forming  a  pocket  for  the 
lodgment  of  debris,  and  thus  gives  rise  to  serious  dif&culties. 
Facets  formed  by  inter-proximate  wear  may  be  found  in  any 
collection  of  teeth.  Exceptionally  cases  are  met  with  in 
which  the  teeth  stand  so  widely  apart  that  they  are  self 
cleaning.  The  form  of  the  inter-proximate  space  is  very 
variable.  The  forms  best  suited  to  the  maintainance  of  the 
health  of  the  teeth  and  gums  are  so  important  to  the  student 
of  operative  dentistry  that  they  should  be  very  closely  studied. 
It  is  best  studied  in  skulls  in  which  the  teeth  are  all  present, 
by  careful  selection  and  arrangement  of  teeth  with  their  roots 
in  wax,  gutta-percha,  or  plaster,  to  hold  them  in  normal  rela- 
tion to  each  other,  and  by  careful  consideration  of  the  forms 
of  the  proximate  surfaces  of  the  teeth  together  with  their 
relative  positions. 

THE   ALVEOLAR   PROCESS   AND   ALVEOLI. 

196.  The  alveolar  process  is  the  projecting  portion 
of  the  maxillary  bones  within  which  the  roots  of  the  teeth 
are  lodged  in  alveoli,  or  sockets,  accurately  fitted  to  their 
surfaces  (Figs.  137  and  138).  The  form  of  the  alveolar  pro- 
cess seems  to  depend  on  the  teeth,  the  conformation  of  their 
roots,  and  their  arrangement  in  the  arch.  If  any  teeth  are 
misplaced,  or  from  any  cause  stand  out  of  the  regular  and 
normal  line,  the  alveolar  process  is  formed  about  their  roots 


Fig.  137. 


Fig.  138. 


Fig.  139. 


Fig.  137*  (Par.  196).— Horizontal  Section  of  the  Alveolar  Process  and  Roots  op 
THE  Teeth  of  the  upper  Jaw,  showing  the  roots  of  the  teeth  in  position. 

Fig.  138*  (Par.  196).— Horizontal  Section  of  the  Alveolae  Process  and  Roots  of 
THE  Teeth  of  the  lower  Jaw,  showing  the  roots  of  the  teeth  in  position. 

Fig.  139*  (Par.  197).— The  Teeth  and  Lingpal  Portion  of  the  Alveolar  Pp.ocess 
OF  the  Upper  Jaw,  and  the  Bones  of  the  Roof  of  the  Mol'th. 


*  Illustration,  actual  size. 


THE    ALVEOLAR   PROCESS   AND   ALVEOLI.  151 


in  this  irregular  position.  Also,  when  teeth  are  lost,  the 
alveolar  process  mostly  disappears  by  absorption,  and  the 
remaining  portions  of  the  alveoli  are  tilled  with  bone. 

197.  Normally,  the  alveolar  process  envelopes  the  roots 
of  the  teeth  to  within  a  short  distance  of  the  gingival  line 
(Figs.  131  and  139),  varying  from  one  to  three  millimeters 
in  the  young  adult.  This  distance  increases  somewhat  with 
increasing  asje.  The  borders  of  the  alveolar  process  are  re- 
duced  to  a  thin  edge  about  the  necks  of  the  teeth  on  both 
the  labial  and  lingual  sides  of  the  incisors  and  cuspids  of 
the  upper  jaw.  About  the  lingual  sides  of  the  necks  of  the 
bicuspids  and  molars  the  borders  are  also  reduced  to  a  thin 
edge,  becoming  slightly  thickened  about  the  second  and 
third  molars,  especially  the  latter.  On  the  buccal  sides  of 
these,  a  thickening  of  the  immediate  borders  of  the  alve- 
olar process,  in  the*  form  of  a  marked  ridge,  begins  about 
the  first  or  second  bicuspid,  more  commonly  between  these 
two,  and  extends  to  the  distal  of  the  third  molar  (Fig. 
131,  a).  This  ridge  varies  in  difierent  examples,  from  a 
very  slight  thickening  of  the  immediate  border,  to  a  thick- 
ness of  two  or  three  millimeters.  It  forms  a  border  stand- 
ing squarely  out  Irom  the  necks  of  the  teeth.  The  alveolar 
process  then  thins  aAvay  so  that,  in  many  instances,  the  buc- 
cal roots  of  the  teeth,  especially  the  mesial  root  of  the  first 
molar,  have  but  a  thin  covering  of  bone. 

198.  Anteriorly,  the  bony  covering  of  the  roots  of  the 
upper  incisors  presents  much  variety.  In  some  examples, 
the  middle  portion  of  the  roots  has  but  a  slight  covering  of 
bone,  but  more  generally  it  is  progressively  thickened  from 
the  neck  to  the  apex.  The  roots  of  the  cuspids  are  prominent 
toward  the  lip,  and,  for  most  of  their  length,  have  only  a 
thin  bony  covering,  and  this  forms  a  ridge  along  the  line  of 
the  root,  which  may  easily  be  traced  with  the  finger  through 
the  soft  tissues  of  both  the  gum  and  lip.  In  many  instances, 
the  bony  covering  is  entirely  wanting  for  a  little  space  near 


« 

152  THE   ALVEOLAE   PROCESS   AND   ALVEOLI. 

the  middle  of  the  length  of  the  root  of  the  cuspid,  the  buccal 
root  of  the  first  bicuspid,  the  mesial  root  of  the  first  molar, 
and,  occasionally,  of  other  teeth. 

199.  On  the  lingual  side  of  the  upper  teeth  (Fig.  139), 
the  progressive  thickening  of  the  alveolar  process,  from  the 
border  toward  the  apex  of  the  root,  is  much  greater;  so 
that  the  roots  of  the  teeth  seem  to  lie  toward  the  labial  and 
buccal  side  of  the'alveolar  process  (Fig.  137).  Even  the  large 
lingual  root  of  the  upper  first  molar,  diverging  strongly  to 
the  lingual,  seldom  forms  a  ridge  or  prominence  of  the  pro- 
cess covering  its  lingual  surface. 

200.  The  anterior  palatine  foramen  is  in  the  median 
line,  just  behind  the  central  incisors  (Fig.  139).  It  is  funnel- 
shaped  with  a  broad  opening  to  the  palatine  surface  of  the 
bone.  The  bone  is  often  quite  thin  between  this  and  the 
roots  of  the  central  incisors.  The  posterior  palatine  artery 
runs  in  a  deep  groove  in  the  surface  of  the  bone,  very  close 
to  the  apex  ot  the  lingual  roots  of  the  upper  third,  and  the 
upper  second  molar.  This  artery  is  occasionally  wounded, 
or  cut,  in  eftbrts  to  extract  the  roots  of  these  teeth. 

201.  In  the  lower  jaw,  the  immediate  borders  of  the 
alveolar  process,  on  the  labial  sides  of  the  incisors,  are  rather 
thicker  than  in  the  upper  jaw,  often  amounting  to  a  decided 
ridge.  This,  however,  thins  away  rapidly,  so  that  the  middle 
portion  of  the  root  has  but  a  thin  covering  of  bone.  At  the 
cuspid,  the  border  of  the  alveolar  process  is  very  thin,  but  a 
gingival  ridge,  corresponding  with  that  of  the  upper  jaw, 
though  not  so  prominent,  begins  at  about  the  first  or  second 
bicuspid  and  runs  1o  the  second  molar.  This  thins  away 
over  the  middle  of  the  length  of  the  roots  of  the  bicuspids  and 
first  molar.  At  the  second  lower  rtiolar,  the  rising  of  the 
external  oblique  ridge  for  the  formation  of  the  anterior  bor- 
der of  the  coronoid  process  (Fig.  131,  6),  causes  a  thickening 
of  the  buccal  bon}^  covering  of  the  root,  while  at  the  third 
molar  this  ridse  rises  to  a  level  with  the  border  of  the  alveolar 


Fig.  140. — Actual  size. 


Fig.  141.— Actual  size. 


Fig.  140  (Par.  202).— Lower  Teeth  and  Maxilla,  as  seen  from  above. 
Fig.  141  (Par.  210).— The  Labial  and  Buccal  Aspect  of  the  Teeth  and  Gums  op 
THE  Upper  Jaw. 


THE    ALVEOLAR    PROCESS    AND    ALVEOLI.  155 

process,  making  the  bony  covering  on  the  buccal  side  of 
the  root  about  one-fourth  of  an  inch  thick  (Fig.  138).  This 
is  of  importance  with  reference  to  the  extraction  of  the  roots 
of  this  tooth.  Indeed,  the  second  and  third  molars  of  the 
lower  jaw  are  fixed  in  alveoli,  hollowed  out  in  the  lingual 
side  of  the  body  of  the  bone  rather  than  in  a  process  or  ridge 
on  the  bone,  as  with  the  teeth  anterior. 

202.  On  the  lingual  side  of  the  lower  anterior  teeth, 
the  border  of  the  alveolar  process  is  a  smooth  thin  edge,  and 
the  covering  of  bone  over  the  roots  progressively  thickens 
toward  their  apexes.  In  this  portion,  the  process  is  high, 
and  the  labio-lingual  thickness  is  only  sufficient  to  envelop 
the  roots  of  the  teeth  and  give  them  support  (Figs.  140  and 
142).  From  the  first  bicuspid  backward  the  height  of  the 
alveolar  process  diminishes  rapidly,  and  the  line  of  the  dental 
arch,  and  of  the  alveoli  of  the  teeth,  passes  diagonally  across 
the  line  of  the  curve  of  the  body  of  the  bone  from  the  buccal 
side  at  the  first  bicuspid  to  the  lingual  side  at  the  third 
molar,  and  sinks  into  the  body  of  the  bone  (Figs,  140  and 
142).  The  border  of  the  alveolar  process  remains  thin  as  far 
as  the  first  or  second  molar,  but  the  bony  covering  of  the 
roots  is  rapidly  thickened  toward  their  apexes. 

203.  This  is  caused  largely  b}^  the  thickening  of  the 
body  of  the  bone,  produced  by  the  rise  of  the  mylohyoid 
ridge  (Fig.  142,  a),  which  begins  in  front  below  the  apexes 
of  the  roots  and  rises  progressively  backward  nearly  to  the 
border  of  the  alveolar  process  at  the  third  molar.  The 
greatest  thickness  is  over  the  lingual  side  of  the  apical  half 
of  the  roots  of  the  second  molar,  and  of  the  crossing  of  the 
lingual  side  of  the  coronal  half  of  the  roots  of  the  third 
molar.  At  the  third  molar  this  ridge  is  thinner,  and  at  the 
distal  angle  often  very  slight,  while  the  lingual  covering  of 
the  roots  of  the  tooth  may  be  very  thin  below  this  ridge. 
Therefore,  it  is  usually  easy,  when  necessary  in  extracting, 
to  force  the  roots  of  the  lower  third  molar  to  the  linsual 


156  THE    PERIDENTAL   MEMBRANE. 

and  distal  with  a  lever  suitably  arranged  against  the  crown 
of  the  second  molar,  as  with  the  Physic's  forceps,  or  an  ele- 
vator. 

204.  The  borders  of  the  septa  of  the  alveoli  of  the 
roots  of  the  anterior  teeth  are  rounded,  or  arched  labio-lin- 
gually,  but  this  diminishes  rapidly  from  the  cuspid  back- 
ward. Between  the  molars  it  is  a  straight  line,  or  presents 
but  a  slight  concavity  so  that  the  highest  points  of  the  bor- 
der of  the  alveolar  process  are  on  the  buccal  and  lingual  sur- 
faces, or  at  the  angles,  of  the  necks  of  these  teeth,  which  is 
important  in  fitting  bands  of  crowns  or  any  similar  pro- 
cesses. 

205.  The  alveolar  process  is  composed  of  an  outer  and 
an  inner  plate  of  moderately  compact  bone,  and  l)etween 
these,  very  open  cancelous  or  spongy  bone ;  so  that  in  young 
persons  it  may  be  forced  more  or  less  to  one  side,  or  bent  out 
of  position,  without  definite  fracture.  The  outer  compact 
plate  forms  the  outer  surface  of  the  bone,  and  the  inner 
plates  line  the  alveoli  of  the  teeth.  These  latter  are  very 
thin,  and  supported  on  all  sides  by  the  cancelous  structure. 
In  the  lower  jaw  the  substance  of  the  bone  is  more  compact 
and  stronger  than  in  the  upper,  especially  about  the  molar 
teeth,  where  the  alveoli  are  in  the  substance  of  the  body  of 
the  bone. 

THE  PERIDENTAL  MEMBRANE. 

206.  The  peridental  membrane  invests  the  roots  of  the 
teeth  from  the  gingival  line  to  the  apexes  of  the  roots  like  a 
sack.  It  lines  every  part  of  the  alveoli,  and,  passing  over 
the  gingival  margins,  is  continuous  with  the  periosteum 
and  gums  covering  the  outer  plate  of  the  alveolar  process. 
It  is  one  membrane,  attached  on  one  side  to  the  root  of  the 
tooth,  and  on  the  other  to  the  inner  wall  of  the  alveolus.  It 
is  composed  of  connective  tissue  which  supports  an  abundant 
supply  of  blood-vessels,  nerves  and  lymphatics.  With  these 
are  intermingled  strong  fibres  of  white  fibrous  tissue  which 


,— Actual  size. 


Fig.  143. 


Fig.  142  (Par.  202).— Lingual  Surface  of  the  Left  Half  of  the  Lower  Maxilla 
AND  Teeth,    a,  Mylo-hyoid  ridge  ;  h,  inferior  dental  foramen. 

Fig.  143  (Par.  211).— Outlines  of  a  Section  of  a  Central  Incisor,  Cut  Lengthwise 
Labio-lingually,  with  its  alveolus  and  appendages  showing  the  relation  of  the  diiTerent 
parts,  a,  Crown  of  the  tooth ;  b,  root ;  c,  c,  bone ;  d,  d,  alveolar  process ;  e.  e,  peridental 
membrane ;  /,  /,  gums ;  g,  g,  gingivje,  or  free  margin  of  the  gums ;  h,  h,  gmgival  line ; 
the  portions  of  the  crown  included  within  the  dotted  lines  i  shows  the  portion  of  the 
proximate  surfaces  covered  by  the  interproximate  gingiva  in  normal  conditions. 


THE   UUMS.  159 


pass  from  the  cementum  of  the  root  of  the  tooth  to  the  boDy 
walls  of  the  alveolus.  The  ends  of  these  are  built  firmly 
into  each,  forming  a  strong  attachment  of  the  root  to  its  alve- 
olus. In  childhood  and  youth,  this  membrane  is  compara- 
tively thick,  and  allows  considerable  motion  of  the  tooth  in 
its  socket.  As  age  advances,  it  becomes  thinner  and  the 
motions  of  the  teeth  are  more  restricted.  A  bundle  of 
nerves  and  one  or  more  arteries  enter  the  alveolus  near  the 
apex  of  the  root  (the  apical  space),  and,  subdividing,  several 
arterial  twigs  and  nerve  bundles  pass  toward  the  giogivte, 
while  others  enter  the  apical  foramen  and  pass  to  the  pulp 
of  the  tooth.  Also,  the  cancelous  portion  of  the  bone  form- 
ing the  alveolar  process  is  richly  supplied  with  blood-vessels 
and  nerves,  and  these  enter  the  alveolus  and  peridental  mem- 
brane from  all  sides.  This  gives  the  peridental  membrane  a 
very  rich  collateral  circulation.  At  the  gingivae,  the  blood- 
vessels become  continuous  with  those  of  the  periosteum  and 
gums.* 

THE  GUMS, 

207.  The  gums  are  the  soft  tissues  covering  the  alveolar 
processes  and  investing  the  necks  of  the  teeth.  They  are 
composed  of  connective  tissue  containing  many  white  fibres 
intermino-led,  forming;  a  firm  membranous  mass,  continuous 
with  the  periosteum  beneath,  and  with  the  peridental  mem- 
brane at  the  necks  of  the  teeth.  They  are  covered  with  a 
strong  outer  coat  of  squamous  epithelium.  They  are  richly 
supplied  with  blood-vessels  and  nerves ;  but,  under  normal 
conditions,  they  are  not  very  sensitive  to  pressure  or  moderate 
violence,  but,  in  pathological  conditions  they  may  become 
very  sensitive. 

208.  On  the  labial  and  buccal  side  of  the  alveolar  pro- 
cess, the  gums  (Fig.  136)  are  thin  and  firm  near  the  necks  of 

*  For  the  details  of  this  subject  the  student  is  referred  to  the  author's  trea- 
tise on  "The  Histological  Characters  of  the  Periosteum  and  Peridental  Mem- 
brane." 


160  THE   GUMS. 


the  teeth  and  strongly  attached  to  the  periosteum.  As  they 
pass  from  the  necks  of  the  teeth  toward  the  base  of  the  alve- 
olar ridge  they  become  softer,  lose  their  close  attachment  to 
the  periosteum,  and  become  merged  into  the  mucous  mem- 
brane of  the  lips  and  cheeks.  In  the  passage  from  the  gums 
to  these  mucous  surfaces  several  loose  folds  are  formed,  the 
most  notable  being  the  frenum  labium  of  the  upper  jaw  at 
the  median  line,  passing  from  near  the  inter-proximate  space 
of  the  central  incisors  to  the  median  line  of  the  upper  lip. 
A  similar,  though  less  prominent  fold  connects  the  median 
line  of  the  lower  lip  with  the  gums.  Occasionally,  folds  of 
less  prominence  are  seen  in  the  neighborhood  of  the  bicuspids 
and  first  molars. 

209.  On  the  lingual  side  of  the  arch  in  the  lower  jaw, 
the  conditions  are  much  the  same.  The  gums  are  firmly 
adherent  to  the  periosteum  near  the  teeth,  but  lower  down 
are  merged  into  the  mucous  membrane  of  the  floor  of  the 
mouth.  The  median  line  of  the  tongue  is  connected  with 
the  median  line  of  the  gums  by  a  strong  fold,  known  as  the 
frenum  linguae.  As  an  abnormal  congenital  condition  this 
is  sometimes  connected  so  near  the  tip  of  the  tongue  as  to 
prevent  its  protrusion  over  the  teeth,  constituting  the  condi- 
tion known  as  tongue-tied.  This  is  generally  corrected  by 
the  muscular  efforts  of  the  tongue,  which  stretch  the  mem- 
brane sufficiently  to  accommodate  its  motions. 

210.  On  the  lingual  side,  in  the  upper  jaw,  the  gums 
(Fig.  127)  are  usually  of  greater  extent  and  thicker.  They 
cover  the  entire  roof  of  the  mouth,  to  the  conjunction  of  the 
hard  and  soft  palate,  as  a  hard  dense  layer.  In  the  anterior 
portion,  a  series  of  irregular  ridges,  known  as  the  rugae, 
radiate  from  the  median  line  toward  both  sides,  stopping 
short  of  the  gingivae.  In  a  large  collection  of  examples 
almost  innumerable  forms  of  these  rugse  may  be  noted. 

211.  The  gingiva  or  gingivae,  is  that  portion  of  the 
gum  tissue  investing  the  neck  of  the  tooth  crownwise  from 


THE   GUMS.  161 


the  attachment  of  the  peridental  membrane  at  the  gingival 
line  (Fig.  143).  It  is  also  termed  the  free  margin  of  the  gum. 
The  length  of  the  gingiva3,  from  the  line  of  attachment  to 
the  neck  of  the  tooth,  varies  in  different  teeth  in  the  same 
mouth,  and  in  different  adults,  from  about  one  to  about  four 
millimeters.  It  is  often  much  greater  in  young  persons,  but 
the  length  usually  diminishes  as  age  advances.  The  free 
margin  fits  around  the  neck  of  the  tooth  closely  ;  but  a  thin, 
flat  instrument  is  easily  passed  between  it  and  the  tooth  to 
the  attachment  at  the  o-ino-ival  line.  As  the  o-ino-ival  line 
of  the  tooth  is  at  the  border  of  the  enamel,  or  at  the  junction 
of  the  enamel  and  cementum,  it  follows  that  the  gingivae  in- 
close the  immediate  gingival  border  of  the  enamel,  and  cover 
this  part  of  the  crown  of  the  tooth.  In  young  persons,  we 
often  see  one-half  of  the  length  of  the  crowns  of  the  teeth 
buried  in  the  gingivae,  even  after  the  teeth  are  regarded  as 
fully  in  place.  As  age  advances,  the  gingivae  become  shorter, 
showing  more  of  the  crown,  and  finally  recede  to  very  near 
the  gingival  line. 

212.  The  gingivae  also  fill  the  inter-proximate  spaces 
in  the  form  of  septa  passing  between  the  teeth  from  labial, 
or  buccal,  to  lingual.  This  portion  of  the  gingiva  is  much 
loncrer  than  that  on  the  labial  and  lingual  surfaces  of  the 
teeth  (Figs.  136  and  143).  In  normal  conditions  it  reaches 
from  the  gingival  line  to  the  contact  point  between  the  teeth, 
completely  filling  the  space  and  preventing  accumulations  of 
debris.  The  form  presented  by  the  gingivae  on  the  labial 
and  buccal  surfaces,  is  a  series  of  imperfect  semi-circles  with 
the  concavity  toward  the  occlusal  surfaces  of  the  teeth,  and 
with  the  points  of  junction  of  these  extending  into  and  fill- 
ing the  inter-proximate  spaces  (Fig.  141).  On  the  lingual 
side  of  the  arch,  the  conditions  are  much  the  same,  but  the 
points  of  the  gingivae  between  the  teeth  are  less  prominent 
(Fig.  127).  As  age  aclvances-and  the  gingivee  recede  toward, 
or  even  to,  the  gingival  line,  the  septa  of  soft  tissue  fail  to 

M 


162  THE   GUMS. 


fill  the  inter-proximate  spaces.  This  may  induce  patholog- 
ical conditions  by  affording  space  for  lodgment  of  debris  in 
pockets,  which  favors  fermentation.  A  like  condition  is  also 
induced  frequently  by  a  faulty  form  of  proximate  contact,  or 
through  the  flattening  of  the  contact  points  by  wear,  which 
allows  food  to  be  forced  into  the  inter-proximate  space,  and 
break  down  the  gum  «eptum  by  its  pressure. 


INDEX. 

THE  NUMBERS  REFER  TO  THE  PARAGRAPHS. 

Alveolar  process 196 

— at  the  buccal  side  of  the  lower  third  molar 20  r 

— bone  forming  the  205 

— borders  of ig7 

— buccal  ridge 19 ; 

— lower  labial  portion 2or 

"       lingual  portion 202 

— relation  of  the  mylohyoid  ridge 203 

"           "        oblique  ridge 201 

— septa  of  the 204 

— upper  labial  portion 198 

"      lingual  portion igg 

Alveoli 196 

"     — relation  of  the  roots  of  the  teeth 197 

Angles — of  the  teeth ,  how  named 7 

"             "      surfaces  of  the  teeth,  how  named 7 

Apical  foramen 153 

Apex  of  the  root  defined 3 

Arrangement  of  the  teeth ,. 187 

Bell  crowned  teeth 14 

"          "              "    — inter-proximate  spaces 194 

Bicuspids 41 

— buccal  surface  of  the  lower  first .- 57 

"             "           "            "      second 63 

"            "          "       upper  first 46 

"            •■          ■'          "       second 52 

— distal  surface  of  the  lower  first 58 

"            "          "          "      second 64 

"            "          "      upper  first 49 

"            "          "        "      second 52 

— grooves  of  lower  first 54-55 

"        "       "      second '. 62 

"        "  upper  first 45 

"        "       "      second 51 

— lingual  surface  of  the  lower  first 59 

"    second 63 

"             "             "        upper  first 47 

"            "            "            "       second 52 

163 


164  INDEX. 


Bicuspids — mesial  surface  of  the  lower  first 58 

"                "            "          "          "       second 64 

"                 "             "           *'       upper  first 48 

"                "            "          "          "       second 52 

*'        — occlusal  surface  of  lower  first ,  54 

"                  "            "        "       "       second 62 

"                  "            "        "    upper  first. 42 

"                  "            "         "        "       second 51 

"        — plan  of  the  formation 41 

"        — root  of  lower  first 61 

"               "      "       "      second 65 

"              it      It    ^^ppgj.  gj-st '.  50 

"              "      "        "       second 53 

"        — ridges  of  lower  first 54-56 

•'               "         "      "       second , 62 

"               "         "  upper  first 43-44 

"               "         "       "      second 51 

"        — lower  first 54 

"                "      second 62 

"        — upper  first 42 

"               "       second 51 

Characteristics  common  to  all  of  the  teeth 3 

Cingulum 18 

Color  of  the  deciduous  teeth  133 

Contact,  proximate 195 

Crown  surfaces 3 

Crowns  of  the  teeth 3 

"         "     "   lower  incisors 6 

"         "     "   deciduous  teeth 130 

Cutting  edge  of  the  incisors 6 

Curvature  of  the  gingival  line 3 

Cusp  defined 8 

Cuspid,  lower 38 

"            "    —ridges 39 

"             "    — similarity  to  the  upper 38 

"             "    — surfaces 38-39 

"             "    — root 40 

upper 33 

' '            "     — distal  surface 36 

"            "     — labial  surface 33 

"      "dge 33 

"            "    — lingual  surface 34 

"            "     — mesial  surface 35 

'            "     —ridges 34 


INDEX, 


165 


Cuspid,  upper— root 37 

Deciduous  first  molars  a  distinct  class 129 

"           second  molars 129 

"           teeth  128 

"              "     — by  what  teeth  succeeded 129 

"               "     — buccal  surfaces 132 

"               "     — color J33 

"              "     — lingual  surfaces 132 

"              "     — crowns 130 

"               "     — necks 131 

•'              "     — number 128 

"               "     — roots 151 

"         molars — lower  first  buccal  surface 148 

"            "              "         "    bucco-gingival  ridge 148 

"            "             "         "     cusps 148 

"             "              "         "'   distal  surface 149 

"            "              "         "     fossae 141 

"            "             "         "    grooves 142 

"             "               "         "     lingual  surface 149 

"             '*              "         "    lobes. 142 

"             "              "         "     mesial  fossa 147 

"             "              "         "         "       surface 149 

"             "              "         "     occlusal  surface 141 

"             "              "         "    principal  fossa 146 

"             "             "         "    ridges 143 

"             "        upper      "     buccal  surface 138 

"            "            "          "     bucco  gingival  ridge ..  138 

"            "          "     cusps 136 

"            "            "          "    distal  surface 140 

"            "            "          "     grooves 135 

"            "             "          "    lobes 135 

"             "             "          "     lingual  surface 140 

"             "             "          "     mesial  surface 140 

"            "            "          "    occlusal  surface 134 

"            "          "    ridges 136 

Dental  arch   187 

' '      formulae 

Developmental  grooves  defined 

"  "of  the  incisors  and  cuspids 

"  "  "      molars 

"  lines  defined 

"  "      of  the  incisors  and  cuspids 

"  "         "       first  upper  molar 


I 
II 
21 
98 
II 

2C 

98 


Dissections , 158 


166  INDEX. 


Dissections — instruments  necessary  for 158 

"        of  the  bicuspids 166 

"             "       incisors 159 

"             "      lower  molars 179 

"             "       upper  molars 171 

Fissure  defined 11 

Fissures,  how  formed 21 

Foramen,  apical 155 

Formulas,  dental i 

Fossa  defined 10 

Frenum  labium 2c8 

"       linguae 209 

Gingivae 2x1 

"     — inter-proximate  spaces 212 

Gingival  groove  and  fissure  of  the  upper  lateral  incisor 26 

"       line,  curvature  of  the 3 

"          "    defined 3 

"          "     of  the  upper  central  incisor 20 

Groove  defined 11 

"          "       developmental 11 

"          "       sulcate II 

"          "       supplemental 12 

Gums 207 

"     labial  and  buccal 208 

"     lingual  of  lower  jaw   209 

"           "         "  upper  jaw 210 

"    of  what  composed 207 

Incisors,  lower 29 

"           "     — developmental  lines 30 

"            "     -T-diflference  between  central  and  lateral 29 

"            "    — distal  surface 30 

"            "     — form  of  crown 29 

"            "     — labial  surface 29 

"            "    — lingual  surface 30 

"            "     — linguo-gingival  ridge 30 

"            "     — mesial  surface . .  30 

"            "     — roots .  31 

"       upper  central 16 

"            "           "       — distal  surface 19 

"           "           "       — developmental  lines  or  grooves 21 

"            "            "       — fissures 21 

"           "           "       — form  of  crown 16 

"           "           "       — gingival  line 20 

"           "            "       — labial  surface 17 


INDEX.  167 

lucisors,  upper  central — lingual  fossa i8 

pit 21 

"             "               "        surface i8 

"             "     — liuguo-giugival  fissure 21 

"              "            "        ridge 18 

"            "     — lobes  of  crown 21 

"             "     — marginal  ridges 18 

"             "     — mesial  surface 19, 

"             "     — root 22- 

' '       lateral 23 

"             "     — distal  surface 25, 

"             "     — division  of  lingual  lobe 26 

"             "     — failure  of  lingual  lobe 26 

"             "     — general  form  of  crown 23 

"             "     — how  different  from  the  central 23 

"             "     — labial  surface 24 

"            "    — lingual  pit 26 

"             "              "         surface 26 

"             "     — linguo-gingival  fissure 26 

"             "     — mesial  surface 25 

"             "     — marginal  ridges 26 

"             "     — root 27 

Inclination  defined igi 

"            mesial — of  the  lower  teeth 192 

"                 "              "        upper  teeth 191 

Inter-proximate  spaces ]  93. 

"                      "      defined 13. 

"                       "       — relation  to  the  forms  of  the  teeth 194. 

Introduction . .      i 

Lines — developmental ir 

"                     "            — of  the  incisors 21 

Lobes  defined 11 

"     of  the  incisors 21 

Lingual  pit  of  the  lateral  incisor 26 

Linguo-gingival  ridge  of  the  incisors 18,  21 

"             "             "         "         cuspids 34 

"             "          groove 21 

Long  cusped  teeth 14 

Lobes  of  the  incisors 21 

Man's  diet i 

Marginal  ridges 9 

Mesial  surface  defined 5 

Measurements  of  the  teeth 15 

"     —tables  of 15 


168 


INDEX. 


Mesial  inclination  of  the  lower  teeth 191,  192 

"  "  "       upper    "     191,192 


Molar,  lower  first. 


— buccal  pit 

' '        gro  Dve 

"        surface 

— central  fossa 

— cusps 

— developmental  grooves. ... 

— distal  surface 

— fissures  

— grooves 

— lingual  surface. 

— mesial  surface 

"      supplemental  fossae 


96 

104 

104 

104 

98 

.100,  loi,  102 

98 

107 

103 

98 

105 

106 

lOI 


-occlusal  surface 96,  98 


-pits 

-triangular  ridges, 
-root 


second 


— buccal  surface 

— cusps 

— developmental  grooves. 

— distal  surface. 

— fissures 

— lingual  surface 

— lobes   

— mesial  surface . 

— occlusal  surface 

— pits 

— root 

— supplemental  fossae 

"  grooves.  . 

— transverse  ridges 

— triangular  ridges 

— variations  of  form 


third. 


— buccal  surface.  . 
— distal  surface. . . 

— five  lobed 

— four  lobed 

— grooves 

— lingual  surface.  . 
— marginal  ridges. 


108 
102 
108 
109 

115 
112 
III 
118 
114 
116 
III 
117 
no 
112 
119 
112 
112 

1X2 
112 

"3 
120 

125 
126 
124 
121 
122 
126 
122 


INDEX.  169 

Molar,  lower  third — mesial  surface 126 

"          "        "    —root 127 

"           "         "    — supernumerary  cusps 123 

"          "        "    — supplemental  fossae 121 

Molar  triangle,  typical  forms .  -. 173 

Molars 66 

' '     — number  and  names 66 

"     — upper 67 

Molar,  upper  first 68 

"           "         "   — buccal  surface 78 

"           "        "   — calcification  of  lobes 69 

"—cusps ••.71,72,73,74 

"           "         "   — distal  surface 81 

"         "   —fifth  lobe 70 

"           "        "—fossae 68 

"           "         "  — grooves 68 

"           "        "  — lingual  surface 79 

"-lobes..... 68 

" .          "         "   — mesial  surface 80 

"           "         "   — occlusal  surface 68 

"           "         "   — oblique  ridge 75 

"        "  —ridges 71,  72,  73 

*'           "    second 86 

"           "         "      — abnormal  forms 87 

"            "         "       — buccal  surface 88 

"            "         "       — central  fossa 86 

"         "      —distal  fossa 86 

"      surface.. 88 

"           "         "      — form  of  neck 89 

"           "         "       — lingual  surface 88 

"            "         "       — mesio-buccal  ridge 89 

**           "         "       — mesial  surface   88 

"           "        "      — occlusal  surface 86 

"           "         "      —roots 90 

*'           "        "      — three  cusped 86 

"           "         "      — variations  of  the  disto-lingual  lobe 86 

*'           "     third 91 

"           "         "     — buccal  surface 93 

"           "         "     — distal  surface   93 

*'            "         "     — disto-lingual  cusp 91 

"            "         "     — irregular  forms 91 

"           "         "     — lingual  surface 93 

"         "     — mesial  surface 93 

"           "         "     — multiple  roots 94 


170 


INDEX. 


Molar,  upper  third — occlusal  surface 

"    —root 

"  "         "     — three  cusped 

"  "         "    — variations  of  form 

Neck  of  a  tooth  defined 

Nomenclature 

Number  of  teeth  of  man 

Occlusal  surface  defined 

Occlusion  line 

"         — relation  of  the  lower  and  upper  teeth 

"  — relative  mesio-distal  position  of  the  teeth. . , 

Peridental  membrane 

Proximate  contact o 

"  "      defined 

"         surfaces  defined 

Pulp  chamber 

"  "        —abnormally  long  horns 

"  "        — conditions  which  cause  diminished  size. 

"  "         — diminished  size  of,  in  the  adult 

*'  "        — dissections  necessary  to  show 

'  *  "        — divisions 

"  ' '         — early  formative  stages .  . ., 

"  "        — forms 

"  "        — in  single  rooted  teeth 

"  "        — lateral  openings 

"  "         of  the  upper  incisors 

"  "  "       lower  incisors 

"  "  "      upper  cuspids 

"  "  "      lower  cuspids 

"  "  "       upper  first  bicuspid 

"  "  "  "       second  bicuspid 

"  "  "       lower  bicuspids 

"  "  "       upper  molars 

"  "  "       lower  molars 

"  "  "      deciduous  teeth 

"  "        — secondary  formations 

"  ' '        — shortening  of  the  horns 

"  "        — variations  in  the  form . 

Ridges  defined 

' '       — how  named 

' '       — marginal 

' '       — transverse 

"       — triangular 

Roots  of  the  teeth  defined 


91 

94 
91 
91 

I 

2 

4 

189 

18S 

190 

206 

195 

5 

5 

152 

185 

155 

154 

157 

153 

154 

153 

156 

1S4 

160 

164 

163 

165 

167 

16S 

169 

172 

180 

18& 

183 

154 

183 

9 

9 

9 

9 

9 

3 


INDEX.  171 


Roots  of  the  teeth — divisions 3 

Root  canal 153 

"         "     — distal,  of  the  lower  molars 182 

"        "            "         "        upper  molars 176 

"         "    — lateral  openings 184 

"         "     — lingual,  of  the  upper  molars 174 

"         "     — mesial ,  of  the  upper  molars 175 

"         "     of  the  bicuspids,  lower 170 

"         '<        <(              (<            upper  first  167 

"      second 168 

"         "       "        cuspids,  lower 165 

"        "       "             "        upper 163 

"         "       "        incisors,  lower 164 

"         "       "             "        upper 161 

"         "       "        molars,  lower 181 

"         "       "              "       upper 173 

"         "     — size  of,  in  the  incisors 162 

"         "    — position  of,  in  the  upper  molars 173 

"         "    — upper  first  molar 173 

"         "            "      second  molar 177 

"         "             "      third  molar 178 

<<        "    — variations  of  the,  in  the  upper  molars 177 

Short  cusped  teeth 14 

Spaces,  inter-proximate 193 

"                "                  defined 13 

Sulcate  groove  defined 11 

Sulcus  defined 10 

Supplemental  grooves  defined 12 

Surfaces,  mesial  and  distal,  defined 5 

"        occlusal,  defined - .' 7 

"        of  the  crown,  named 4 

•'        proximate,  defined 5 

Tables  of  measurements  of  the  teeth 15 

Teeth — arrangement 187 

"     — number 2 

Thick-necked  teeth 14 

Thirds — division  of  crown  into 5 

Tissues  of  the  teeth 2 

Tongue-tied 209 

Transverse  ridges  defined 9 

Triangular  ridges  defined • 9 

Tubercle  defined 9 

Wrinkles  defined 12 


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